Hey, Angie, you should consider DDR hottest party instead, which is already out for Wii and has a broader teen appeal than the mario DDR does.  Your big title will likely be Super Smash Brothers Brawl, which has just been delayed until February... that game alone will likely keep you buried in teenage boys everytime you set it up.

Wii play is fun but is only two players; but Mario Party 8 is quite good and is great for events for elementary and younger middle schoolers.  However, the title you should not miss for that audience is Pokemon Battle Revolution.  Kids can link up their DS's and play against each other on the big screen.

One other great title for multiplayer fun is Wario Ware; lots of bizarre minigames and great for teens.  Madden for Wii is also an interesting twist on the football control schemes and most people really love it.  Finally, consider Rayman Raving Rabids, which is yet another minigame collection, but very silly, just a little cool, and usually popular with teens, and Big Brain Academy, which has even more minigames and some great multiplayer modes.

Good luck and enjoy!

-eli