If KeyHit(KEY_A) Then 'Do something!
If KeyHit(KEY_F1) Then 'Do something!
If KeyHit(MODIFIER_CONTROL) Then 'Do something!
If KeyHit(MODIFIER_ALT) Then 'Do something!
etc..
If you go to the documentation for KeyDown() or KeyHit() there should be a link to 'key codes' (a list of valid key codes).