Definitely get Bomberman, I'll say that straight out. You have a Wii, so you're bound to get friends wanting to play, and it's actually the best multiplayer game on the Wii.
Otherwise, it depends on what you've played already really. If you've never owned a Nintendo console before, my god, there's an absolute ton of great stuff on there to play already. Get the top rated stuff like the Marios and the Zeldas first, because they aren't to be missed.
I'm a bit of a multiplayer nut, so I'd recommend things like Streets of Rage, Gain Ground, Golden Axe, Mean Bean Machine, Mario Kart and Gunstar Heroes as well, but that's up to you really. Have a look on somewhere like GameRankings if you've no idea what's good or not, and pick the best rated games.