Splinter Cell DS has a Co-op (and versus) mode.
I, being a fan of the SC series, quite enjoyed this game (although I can tell you that not everybody did, mainly cause it's framerate).
When I finished it, I was so hoping that one day I would find someone with a DS, and force him to buy SC DS. Suddenly, I discovered that a guy I know actually had a DS with Splinter Cell, for allmost a year.. XD
I played the Co-op and it's nice (again, if you like the main game, you'll like the multiplayer).