The VGChartz list of the best co-op games for every system ever.

[crumas2]

Dallinor said:
List of great PS2 co-op games:

Time Splitters 2
Baldur's Gate: Dark Alliance
Dynasty Warriors 4
Half:Life
Twisted Metal: Black
Tenchu 3: Wrath Of Heaven
The Sims

Amen to Dark Alliance... that game rocks in co-op.  I liked Return to Arms as well.