PC games that are worth a play (on the cheap)

Can you recommend me some PC games that are worth playing for around £15 or less.

Im thinking of picking up Black and White 2 tomorrow since i loved the first one.

Any ideas?

EDIT:

My PC specs are - Athlon 64 3200, 1GB RAM, 6600 GT 128MB

Morrowind, Half life 2 (with the orange box out, you should be able to get this for cheap), Guild Wars (maybe more than 15, but u'r gonna play if for hundreds of hours)siafni

Ive played Morrowind and bloody loved it lol, i have HL 2 Orange Box and i couldn't really get into Guild Wars tbh

no one lives forever 1 & 2. vampire: the masquerade - bloodlines. sam & max season 1. f.e.a.r. bg 1 & 2 + expansions. fallout 1 & 2. not sure how much they're in england, but they're all cheap in the u.s.fireandcloud

Played no one lives forever 1 & 2, not really interested in bloodlines or sam and max. Im not sure what 'BG' is.

I think i'll give Fallout a try though.

Thanks!

Most or all of the below are through the Amazon marketplace. They're all mostly or exclusively singleplayer games, so feel free to buy used.

Escape from Butcher Bay is one of the best games ever made, £7.

Vampire the Masquerade Bloodlines is as good as roleplaying games get, £17.

Sam and Max Season 1 is hilarious and brilliant. £13.

Fallout collection is the best deal in the history of computer games, don't listen to IGN. £3.

Doom collector's edition. Games don't get any better. £6