Dungeon Explorer might be a good game to try out. I've got it on NDS and it's pretty good for a dungeon crawler type of game. I'm looking forward to the US version of Phantasy Star Portable, that or a fan-made translation patch like they did with Monster Hunter Portable 2G.
Unfortunately the range is very limited. Most games are geared towards solo play for when you're traveling around, and any multi-player action is purely for head to head battles (take Sonic Rivals for example). Cooperative action is something that has been largely lost since the days of Duke Nukem 64.