Wii:
Metroid Prime Trilogy (great amount of content for the price)
NSMB Wii (it's hard not to find this game fun, also great for the local multiplayer aspect)
Mario Kart Wii
Muramasa
Little King's Story (one of the most fun games on the Wii with lots of gameplay, but doesn't use motion controls)
Mario Strikers: Charged
Trauma Center
Wiiware:
Dr. Mario Online
World of Goo (very addictive, great use of motion controls)
Lost Winds
Gamecube:
Tales of Symphonia
Donkey Kong Jungle Beat
Pikmin
Phantasy Star Online
Sonic Adventure 2: Battle
Resident Evil 1, 0