It's all matter of personal preference, but I strongly suggest for the sake of your own sanity that W, A, S, and D are used for movement as they are in most games. I used to rebind that all to the number pad in every game I played but got sick of rebinding every time I wanted to play a game so I relearned the proper WASD. Also, if you're used to console games and are playing with a joypad, seriously try to learn the mouse, it's awkward at first but in the long run will drastically improve your game.
All the keys directly around WASD are fair game, however. For instance, in WoW I find a lot of default keys set to do stupid things, like "c" brings up the character screen, "x" sits, "z" unsheathes. "q" and "e" unnecessarily strafe left and right. These are horrendous wastes of keys which should be used for important spells (save the "clicking" for bringing up menus). WoW doesn't require the same precision as an FPS, however the same applies to any game where you have multiple functions. Quick-switching weapons with "q" is good in GES, but kind of vital in Counter-Strike (and decedents).
In summary, use WASD for movement, and the easiest keys for you to press that are nearby for important functions. Avoid sacrificing freedom of strafing to voice-chat or anything else that requires extended holding down of a badly positioned key, though.
Also, I used to use "ALT" to crouch in CS... that's bad because sometimes when you check the scoreboard, you die. It's an easy key for voice-chat... but "TAB" still brings up the scoreboard... lol
