4 for £20 at Blockbuster
The 4 for £20 preowned games section at my local Blockbuster had a pretty good selection of games:
Viva Piñata: Trouble in Paradise, Xbox 360
Far Cry 2, Xbox 360
Unreal Tournament 3, PS3
Rhythm Paradise, DS
Advance Wars: Dark Conflict, DS
Final Fantasy 3, DS
Dragon Quest IV: Chapters of the Chosen
Nothing to set the world on fire, but cheaper than buying most of them on their own.
