Load and Loads of pre-owned games to choose from.
For the PS2, XBOX, GameCube and GameBoy Advance. Gamestation are selling these games at £7.99 each or 4 for £20. You'll need to have a look through the lists but there seem to be a few good games, lots to suit most tastes.
Also they are doing another promo for 2 for £20 with some newer titles, worth a look if you want something a bit more recent.http://www.gamestation.co.uk/images/category/pre-owned-2for20.asp
These deals are also available in their shops if you live close by one, although the selections on offer will most likely be a little more limited.