1-9 keys for weapons. Tab for scoring/inventory or something like that. F1-F12 are sometimes used for non-conventional abilities eg. force powers in Star Wars or plasmids in BioShock.
Also, I like using z for zoom. C can be used for crouch but it should be toggled (rather than held) since you can't move very well with WASD if you're holding C. The . and , keys, or the [ and ] or ; and ' keys (on a UK keyboard, anyway) can be used to cycle weapons. T could be used to switch camera, but it sounds like you'd be using first person the whole time.
Secretary of Unknowable Knowledge for the Rock/Dink administration '08