Super Mario Galaxy is *lots *of fun.
And that’s all I got to say about that. 
My kids got me Samba De Amigo for Christmas, and it’s a lot of fun. You use the Wiimote and nunchuck as maracas, and the game has a bunch of fun music. You can also download extra music packs from the Wii store. Multi-player is fun, and each player gets to set their difficulty level which makes it fair for the kids to play against me or mom.
My kids are addicted to Mario Party 8. It’s board-game style, with mini-games thrown in between each round. Again, the multi-player is what they like best - with 4 Wiimotes, we can all play together
Moved to The Game Room.
Keep in mind that if you buy the charging stand for the Wiimotes, you have to remove the silicon skins to put them in. IMHO, it’s easier to just use the batteries until they need to be replaced, and keep an extra set charged in a conventional charger. If you get the charger for the Wii fit, you’ll have to keep your Wii fit plugged in and your Wii on to keep it charged. We’ve had the Wii fit for over 2 months and have not changed the batteries in it yet, so IMHO, it’s completely unnecessary also.
**Wii Ski **is a fun game if you get the Wii Fit board and like skiing. There are several fun minigames (ski races, moguls, trick jumps, etc.). You can play it without the Wii fit, but then it’s nothing like actual skiing. With the Wii fit, the motion is surprisingly realistic.
I’ve had a Wii for about 6 months, these are the 3 favorites I’ve owned:
Super Smash Brothers- Solid Game. Much better if you’re playing it with other people. I barely touched the online, didn’t seem to be many players available at any given time.
Mario Kart- LOVE THIS GAME. The multi-player feature is fun, the on-line capability works great, and there’s tons to unlock (bikes, characters, etc.) in single-player too.
Boom Blox- I bought this one after reading some threads on here. It’s a fun little physics based game, and lets you use the WiiMote in a variety of ways.
I agree w/ other posters above, World of Goo is definately worth getting too.
Grab Super Smash Brothers, Mario Galaxy, and Mario Kart and you’ll be happy for a good long time. And Okami, if you can find it.
If you’re a fan of Homestar Runner, the StrongBad Wiiware games are great. Also check out Lost Winds, another Wiiware title. The main problem with the Wiiware games is they’re short, but on the other hand, no changing disks.
(looks at thread title)
For God’s sake, try to hold it until you get to the bathroom!
sorry…
I second the World of Goo nomination. I also recently got Boom Blox, which starts off easy and the background graphics are a bit cheesy, but it’s getting more fun and challenging.