GmodeKeys

GmodeKeys is a mod that does the simple thing of stopping the pain of having to write /gamemode creative ( And the other commands ) into a simple shortcut

Shortcuts:

G + C = Creative G + V = Spectator G + B = Adventure G + N = Survival

If you press G 3 times, there will also open up a menu where you can also switch; it also just shows the shortcuts in there.