Super Smash Brothers Brawl is DEFINITELY the best game out there. I've heard Mario Kart Wii was good, but due to errors (or so I've heard) the plant that made them had to shut down. Until when, and if they make the game is again is iffy.
Though Brawl is awesome. 300 songs, allowing you to choose which ones to play how often on each stage. 2p modes are a lot more varying then Melee, and there are tons of fun things to do on wifi.