Good lists so far. You probably have enough already, but if you're still looking for suggestions, how about Bomberman Blast (WiiWare)? If you have gamecube controllers, you can have up to eight people playing at once. Defend Your Castle is cheap and great for 4-players. Tetris Party is fun too...

Now that I think of it, there are a lot of possibilities there. But definitely look into Defend Your Castle, if nothing else (and/or Bomberman, if you have Gamecube controllers. Oh, the sweet chaos...).

Devil may cry ^^

Yer there isn't. I double check I was getting confused with Mercenaries missions, where me and my friends would take turns and compare scores. So in a way we did play against each other but not at the same time. My bad.