One great Wii game that I don't think has been mentioned yet, if you haven't played it already, is Okami. It's an adventure game of sorts where you play as a Japanese goddess in the form of a wolf with the ability to pause time and create things. It's kind of similar to Zelda in terms of gameplay structure, but it has a vastly superior storyline, and the Japanese painting art style is incredible. The soundtrack is beautiful as well.
Outside of that, the four Retro Studios titles (Metroid Prime Trilogy and Donkey Kong Country Returns) are must plays as well, though actually finding a not incredibly expensive copy of Trilogy is hard nowadays. If you get the chance to shop around on the eShop, Super Metroid is well worth the $8.