I would get COD 4 first out of that lot, because you would not only have th esingle player, but a fun multiplayer too, which will keep you busy for longer.
Then get Bioshock as you will have COD 4 for your multiplayer kicks.
Crysis would definitely be last on that list.
Though, and I know some people will disagree with me, but you can get Enemy Territory: Quake Wars for next to nothing these days and the multiplayer can be quite fun. You can pick it up for under £5 on an auction site.