I wanna replace Mono by Visual Studio.
How?
Is it free?
Visual Studio Express is free. Last time I checked you needed Professional or higher to use it with Unity. At least UnityVS (debugging in VS) requires Pro or higher.
You can use Visual Studio C# Express with Unity.
You can also link them together with a simple trick I’ve explained previously:
UnityVS will work with Unity Free but VS pro it seems.
Too bad
I use VS with a free plugin I found on the forum, but it’s not working completely.
I work mostly with Playmaker so it’s not bothering me so much, I do minimal scripting
Ok, I switched to Visual Studio 2010 in the next way:
Edit/Preferences…/External Tools/External Script Editor
lame that the “student” version of VSpro is only for college students… screw college, i dont need it lol!! (but im still a “student”) 
pfftt… their pricing is so bogus… … luckily there IS the express version…
lol express 2010 says “use of this product should be limited to evaluation purposes only”
pfft… screw them! hahaha