GUITEXT over a GUIButton

how can i get a gui text above a gui button,i have tried several thing but the text always appear behind the button

You can't, OnGUI is always on top. Better not to mix GUIText/GUITexture with OnGUI, use one or the other.

OnGUI (all unity gui calls) are executed for the screen space and are always drawn on top of any other things on your screen. there is no consept of layers or ... for them. OnGUI don't take cameras into account and you can not render them for a camera or another, they are something general executed for the final image drawn on the screen.

hopefully the next GUI system that unity will provide will be something more flaexible and can be drawn on textures too.

You can use GUI class purely instead of using combining GUI approach:

function OnGUI () { 
   GUI.Button (Rect (10, 10, 100, 20), "Hello Button!");

   GUI.Label (Rect (10, 10, 100, 20), "Hello Text!");