Multiplayer would be Mario Party 8. And if you have a TV that can make use of the 480p from the Components then they are worth it.
Also:
Super Mario Galaxy
Metroid Prime: Corruption
Resident Evil 4: Wii Edition (if you have not played the original 4)
Legend of Zelda: Twilight Princess
Super Paper Mario
Super Smash Bros.: Brawl and Metroid Prime 3: Corruption are the two games that I really enjoyed. If you're a huge Zelda fan you might like Twilight Princess, although I personally find it a little too boring.
Mario Galaxy
Metroid Prime 3
Zelda Twilight Princess
Okami
No More Heroes
Super Smash Brothers Brawl
Boom Blox
Resident Evil 4 ( if u havent played it already)
Mario Kart
I own all of these games and while I play my Wii very little, I enjoy these games immensely.