Y - Virtual keyboard
B - Menu
X - Presses space key 
A - Presses the attack button 
Start - Presses the enter key  
Select + Left trigger - quicksave (One quicksave per game only)
Select + Right trigger - quickload
Left trigger - CLR/HOME
Right trigger - Run/Stop

Select + Up - Presses F1
Select + Left - Presses F3
Select + Down - Presses F5
Select + Right - Presses F7

Select + brightness key - swap joystick port (if you can not move press this combo 
to make your character move) 
Example of games which need this - Bruce Lee, Ghostbusters

Select + start - Presses the E key 
Menu item - Presses the D key
Select + Y - Presses Y key
Select + B - Presses N key
Select + X - Presses 1
Select + A - Presses 2