It's so hard to find some that you haven't played before anymore!
Current gen has been so into online multiplayer, but it seems a lot of games coming out now have forgot just how much fun getting a bunch of friends over at your house and playing together on one TV can be.
Suggestions? Any and all are welcome! But for me... particularly for these systems?:
Wii (including WiiWare and Virtual Console)
N64 (not every game's on VC yet, of course!)
Some of these are kinda older, but hey, if it's good, it's good!
Oh, and lesser-known stuff especially - mainly because I already own quite a few of the games more well-known for this...