There's tons of videos on YouTube. Here are some of the better ones. Personally, I can't wait for the Wii. It looks tons fun more than the 360 or the PS3.

Wii Teaser
The first Wii commercial. It's a little ridiculous, but definitely got my hyped up for the Wii.
http://www.youtube.com/watch?v=FaUvbncE3Gk&search=wii

Wii Video 1
This is the most recent Wii commercial. Lots of game play. WATCH THIS.
http://www.youtube.com/watch?v=73yDRm8KaWY&search=wii

Wii Video 2
Lots of game play footage and some guy jumping around like an ass. LOTS of game footage....
http://www.youtube.com/watch?v=UrQZZKatGfM&search=wii

Red Steel
http://www.youtube.com/watch?v=52WhHr4Cm00&search=wii%20red%20steele

Super Mario Galaxy
http://www.youtube.com/watch?v=U-Qw1ClCVN8&search=super%20mario%20galaxy