-NEW BEST ANSWER-
Complete list from UNITY (including all 8 20-button joysticks):
None = Not assigned (never returned as the result of a keystroke).
Backspace = The backspace key.
Delete = The forward delete key.
Tab = The tab key.
Clear = The Clear key.
Return = Return key.
Pause = Pause on PC machines.
Escape = Escape key.
Space = Space key.
Keypad0 = Numeric keypad 0.
Keypad1 = Numeric keypad 1.
Keypad2 = Numeric keypad 2.
Keypad3 = Numeric keypad 3.
Keypad4 = Numeric keypad 4.
Keypad5 = Numeric keypad 5.
Keypad6 = Numeric keypad 6.
Keypad7 = Numeric keypad 7.
Keypad8 = Numeric keypad 8.
Keypad9 = Numeric keypad 9.
KeypadPeriod = Numeric keypad ‘.’.
KeypadDivide = Numeric keypad ‘/’.
KeypadMultiply = Numeric keypad ‘*’.
KeypadMinus = Numeric keypad ‘=’.
KeypadPlus = Numeric keypad ‘+’.
KeypadEnter = Numeric keypad enter.
KeypadEquals = Numeric keypad ‘=’.
UpArrow = Up arrow key.
DownArrow = Down arrow key.
RightArrow = Right arrow key.
LeftArrow = Left arrow key.
Insert = Insert key key.
Home = Home key.
End = End key.
PageUp = Page up.
PageDown = Page down.
F1 = F1 function key.
F2 = F2 function key.
F3 = F3 function key.
F4 = F4 function key.
F5 = F5 function key.
F6 = F6 function key.
F7 = F7 function key.
F8 = F8 function key.
F9 = F9 function key.
F10 = F10 function key.
F11 = F11 function key.
F12 = F12 function key.
F13 = F13 function key.
F14 = F14 function key.
F15 = F15 function key.
Alpha0 = The ‘0’ key on the top of the alphanumeric keyboard.
Alpha1 = The ‘1’ key on the top of the alphanumeric keyboard.
Alpha2 = The ‘2’ key on the top of the alphanumeric keyboard.
Alpha3 = The ‘3’ key on the top of the alphanumeric keyboard.
Alpha4 = The ‘4’ key on the top of the alphanumeric keyboard.
Alpha5 = The ‘5’ key on the top of the alphanumeric keyboard.
Alpha6 = The ‘6’ key on the top of the alphanumeric keyboard.
Alpha7 = The ‘7’ key on the top of the alphanumeric keyboard.
Alpha8 = The ‘8’ key on the top of the alphanumeric keyboard.
Alpha9 = The ‘9’ key on the top of the alphanumeric keyboard.
Exclaim = Exclamation mark key ‘!’.
DoubleQuote = Double quote key ‘"’.
Hash = Hash key ‘#’.
Dollar = Dollar sign key ‘$’.
Ampersand = Ampersand key ‘&’.
Quote = Quote key '.
LeftParen = Left Parenthesis key ‘(’.
RightParen = Right Parenthesis key ‘)’.
Asterisk = Asterisk key ‘*’.
Plus = Plus key ‘+’.
Comma = Comma ‘,’ key.
Minus = Minus ‘=’ key.
Period = Period ‘.’ key.
Slash = Slash ‘/’ key.
Colon = Colon ‘:’ key.
Semicolon = Semicolon ‘;’ key.
Less = Less than ‘<’ key.
Equals = Equals ‘=’ key.
Greater = Greater than ‘>’ key.
Question = Question mark ‘?’ key.
At = At key ‘@’.
LeftBracket = Left square bracket key ‘[’.
Backslash = Backslash key ''.
RightBracket = Right square bracket key ‘]’.
Caret = Caret key ‘^’.
Underscore = Underscore ‘_’ key.
BackQuote = Back quote key ‘`’.
A = ‘a’ key.
B = ‘b’ key.
C = ‘c’ key.
D = ‘d’ key.
E = ‘e’ key.
F = ‘f’ key.
G = ‘g’ key.
H = ‘h’ key.
I = ‘i’ key.
J = ‘j’ key.
K = ‘k’ key.
L = ‘l’ key.
M = ‘m’ key.
N = ‘n’ key.
O = ‘o’ key.
P = ‘p’ key.
Q = ‘q’ key.
R = ‘r’ key.
S = ‘s’ key.
T = ‘t’ key.
U = ‘u’ key.
V = ‘v’ key.
W = ‘w’ key.
X = ‘x’ key.
Y = ‘y’ key.
Z = ‘z’ key.
Numlock = Numlock key.
CapsLock = Capslock key.
ScrollLock = Scroll lock key.
RightShift = Right shift key.
LeftShift = Left shift key.
RightControl = Right Control key.
LeftControl = Left Control key.
RightAlt = Right Alt key.
LeftAlt = Left Alt key.
LeftCommand = Left Command key.
LeftApple = Left Command key.
LeftWindows = Left Windows key.
RightCommand = Right Command key.
RightApple = Right Command key.
RightWindows = Right Windows key.
AltGr = Alt Gr key.
Help = Help key.
Print = Print key.
SysReq = Sys Req key.
Break = Break key.
Menu = Menu key.
Mouse0 = First (primary) mouse button.
Mouse1 = Second (secondary) mouse button.
Mouse2 = Third mouse button.
Mouse3 = Fourth mouse button.
Mouse4 = Fifth mouse button.
Mouse5 = Sixth mouse button.
Mouse6 = Seventh mouse button.
JoystickButton0 = Button 0 on any joystick.
JoystickButton1 = Button 1 on any joystick.
JoystickButton2 = Button 2 on any joystick.
JoystickButton3 = Button 3 on any joystick.
JoystickButton4 = Button 4 on any joystick.
JoystickButton5 = Button 5 on any joystick.
JoystickButton6 = Button 6 on any joystick.
JoystickButton7 = Button 7 on any joystick.
JoystickButton8 = Button 8 on any joystick.
JoystickButton9 = Button 9 on any joystick.
JoystickButton10 = Button 10 on any joystick.
JoystickButton11 = Button 11 on any joystick.
JoystickButton12 = Button 12 on any joystick.
JoystickButton13 = Button 13 on any joystick.
JoystickButton14 = Button 14 on any joystick.
JoystickButton15 = Button 15 on any joystick.
JoystickButton16 = Button 16 on any joystick.
JoystickButton17 = Button 17 on any joystick.
JoystickButton18 = Button 18 on any joystick.
JoystickButton19 = Button 19 on any joystick.
Joystick1Button0 = Button 0 on first joystick.
Joystick1Button1 = Button 1 on first joystick.
Joystick1Button2 = Button 2 on first joystick.
Joystick1Button3 = Button 3 on first joystick.
Joystick1Button4 = Button 4 on first joystick.
Joystick1Button5 = Button 5 on first joystick.
Joystick1Button6 = Button 6 on first joystick.
Joystick1Button7 = Button 7 on first joystick.
Joystick1Button8 = Button 8 on first joystick.
Joystick1Button9 = Button 9 on first joystick.
Joystick1Button10 = Button 10 on first joystick.
Joystick1Button11 = Button 11 on first joystick.
Joystick1Button12 = Button 12 on first joystick.
Joystick1Button13 = Button 13 on first joystick.
Joystick1Button14 = Button 14 on first joystick.
Joystick1Button15 = Button 15 on first joystick.
Joystick1Button16 = Button 16 on first joystick.
Joystick1Button17 = Button 17 on first joystick.
Joystick1Button18 = Button 18 on first joystick.
Joystick1Button19 = Button 19 on first joystick.
Joystick2Button0 = Button 0 on second joystick.
Joystick2Button1 = Button 1 on second joystick.
Joystick2Button2 = Button 2 on second joystick.
Joystick2Button3 = Button 3 on second joystick.
Joystick2Button4 = Button 4 on second joystick.
Joystick2Button5 = Button 5 on second joystick.
Joystick2Button6 = Button 6 on second joystick.
Joystick2Button7 = Button 7 on second joystick.
Joystick2Button8 = Button 8 on second joystick.
Joystick2Button9 = Button 9 on second joystick.
Joystick2Button10 = Button 10 on second joystick.
Joystick2Button11 = Button 11 on second joystick.
Joystick2Button12 = Button 12 on second joystick.
Joystick2Button13 = Button 13 on second joystick.
Joystick2Button14 = Button 14 on second joystick.
Joystick2Button15 = Button 15 on second joystick.
Joystick2Button16 = Button 16 on second joystick.
Joystick2Button17 = Button 17 on second joystick.
Joystick2Button18 = Button 18 on second joystick.
Joystick2Button19 = Button 19 on second joystick.
Joystick3Button0 = Button 0 on third joystick.
Joystick3Button1 = Button 1 on third joystick.
Joystick3Button2 = Button 2 on third joystick.
Joystick3Button3 = Button 3 on third joystick.
Joystick3Button4 = Button 4 on third joystick.
Joystick3Button5 = Button 5 on third joystick.
Joystick3Button6 = Button 6 on third joystick.
Joystick3Button7 = Button 7 on third joystick.
Joystick3Button8 = Button 8 on third joystick.
Joystick3Button9 = Button 9 on third joystick.
Joystick3Button10 = Button 10 on third joystick.
Joystick3Button11 = Button 11 on third joystick.
Joystick3Button12 = Button 12 on third joystick.
Joystick3Button13 = Button 13 on third joystick.
Joystick3Button14 = Button 14 on third joystick.
Joystick3Button15 = Button 15 on third joystick.
Joystick3Button16 = Button 16 on third joystick.
Joystick3Button17 = Button 17 on third joystick.
Joystick3Button18 = Button 18 on third joystick.
Joystick3Button19 = Button 19 on third joystick.
Joystick4Button0 = Button 0 on forth joystick.
Joystick4Button1 = Button 1 on forth joystick.
Joystick4Button2 = Button 2 on forth joystick.
Joystick4Button3 = Button 3 on forth joystick.
Joystick4Button4 = Button 4 on forth joystick.
Joystick4Button5 = Button 5 on forth joystick.
Joystick4Button6 = Button 6 on forth joystick.
Joystick4Button7 = Button 7 on forth joystick.
Joystick4Button8 = Button 8 on forth joystick.
Joystick4Button9 = Button 9 on forth joystick.
Joystick4Button10 = Button 10 on forth joystick.
Joystick4Button11 = Button 11 on forth joystick.
Joystick4Button12 = Button 12 on forth joystick.
Joystick4Button13 = Button 13 on forth joystick.
Joystick4Button14 = Button 14 on forth joystick.
Joystick4Button15 = Button 15 on forth joystick.
Joystick4Button16 = Button 16 on forth joystick.
Joystick4Button17 = Button 17 on forth joystick.
Joystick4Button18 = Button 18 on forth joystick.
Joystick4Button19 = Button 19 on forth joystick.
Joystick5Button0 = Button 0 on fifth joystick.
Joystick5Button1 = Button 1 on fifth joystick.
Joystick5Button2 = Button 2 on fifth joystick.
Joystick5Button3 = Button 3 on fifth joystick.
Joystick5Button4 = Button 4 on fifth joystick.
Joystick5Button5 = Button 5 on fifth joystick.
Joystick5Button6 = Button 6 on fifth joystick.
Joystick5Button7 = Button 7 on fifth joystick.
Joystick5Button8 = Button 8 on fifth joystick.
Joystick5Button9 = Button 9 on fifth joystick.
Joystick5Button10 = Button 10 on fifth joystick.
Joystick5Button11 = Button 11 on fifth joystick.
Joystick5Button12 = Button 12 on fifth joystick.
Joystick5Button13 = Button 13 on fifth joystick.
Joystick5Button14 = Button 14 on fifth joystick.
Joystick5Button15 = Button 15 on fifth joystick.
Joystick5Button16 = Button 16 on fifth joystick.
Joystick5Button17 = Button 17 on fifth joystick.
Joystick5Button18 = Button 18 on fifth joystick.
Joystick5Button19 = Button 19 on fifth joystick.
Joystick6Button0 = Button 0 on sixth joystick.
Joystick6Button1 = Button 1 on sixth joystick.
Joystick6Button2 = Button 2 on sixth joystick.
Joystick6Button3 = Button 3 on sixth joystick.
Joystick6Button4 = Button 4 on sixth joystick.
Joystick6Button5 = Button 5 on sixth joystick.
Joystick6Button6 = Button 6 on sixth joystick.
Joystick6Button7 = Button 7 on sixth joystick.
Joystick6Button8 = Button 8 on sixth joystick.
Joystick6Button9 = Button 9 on sixth joystick.
Joystick6Button10 = Button 10 on sixth joystick.
Joystick6Button11 = Button 11 on sixth joystick.
Joystick6Button12 = Button 12 on sixth joystick.
Joystick6Button13 = Button 13 on sixth joystick.
Joystick6Button14 = Button 14 on sixth joystick.
Joystick6Button15 = Button 15 on sixth joystick.
Joystick6Button16 = Button 16 on sixth joystick.
Joystick6Button17 = Button 17 on sixth joystick.
Joystick6Button18 = Button 18 on sixth joystick.
Joystick6Button19 = Button 19 on sixth joystick.
Joystick7Button0 = Button 0 on seventh joystick.
Joystick7Button1 = Button 1 on seventh joystick.
Joystick7Button2 = Button 2 on seventh joystick.
Joystick7Button3 = Button 3 on seventh joystick.
Joystick7Button4 = Button 4 on seventh joystick.
Joystick7Button5 = Button 5 on seventh joystick.
Joystick7Button6 = Button 6 on seventh joystick.
Joystick7Button7 = Button 7 on seventh joystick.
Joystick7Button8 = Button 8 on seventh joystick.
Joystick7Button9 = Button 9 on seventh joystick.
Joystick7Button10 = Button 10 on seventh joystick.
Joystick7Button11 = Button 11 on seventh joystick.
Joystick7Button12 = Button 12 on seventh joystick.
Joystick7Button13 = Button 13 on seventh joystick.
Joystick7Button14 = Button 14 on seventh joystick.
Joystick7Button15 = Button 15 on seventh joystick.
Joystick7Button16 = Button 16 on seventh joystick.
Joystick7Button17 = Button 17 on seventh joystick.
Joystick7Button18 = Button 18 on seventh joystick.
Joystick7Button19 = Button 19 on seventh joystick.
Joystick8Button0 = Button 0 on eighth joystick.
Joystick8Button1 = Button 1 on eighth joystick.
Joystick8Button2 = Button 2 on eighth joystick.
Joystick8Button3 = Button 3 on eighth joystick.
Joystick8Button4 = Button 4 on eighth joystick.
Joystick8Button5 = Button 5 on eighth joystick.
Joystick8Button6 = Button 6 on eighth joystick.
Joystick8Button7 = Button 7 on eighth joystick.
Joystick8Button8 = Button 8 on eighth joystick.
Joystick8Button9 = Button 9 on eighth joystick.
Joystick8Button10 = Button 10 on eighth joystick.
Joystick8Button11 = Button 11 on eighth joystick.
Joystick8Button12 = Button 12 on eighth joystick.
Joystick8Button13 = Button 13 on eighth joystick.
Joystick8Button14 = Button 14 on eighth joystick.
Joystick8Button15 = Button 15 on eighth joystick.
Joystick8Button16 = Button 16 on eighth joystick.
Joystick8Button17 = Button 17 on eighth joystick.
Joystick8Button18 = Button 18 on eighth joystick.
Joystick8Button19 = Button 19 on eighth joystick.