Sin City: The opening credits for Sin City are awesome. They feature pictures of the characters from the comic books next to the actors names. Its really cool, because they show Frank Miller's awesome artwork along with the movie's sexy film score.
Watchmen: These opening credits are amazing because it basically explains everything that happened to the original superheroes along with my favorite Bob Dylan song.
Juno: I guess for these opening credits they filmed Ellen Page walking on a treadmill and used that to animate this really cool looking opening sequence. Also, I really like this song.
Tropic Thunder: Tom Cruise dancing to Ludacris. Awesome graphics. 'Nuff said. Not a very good video, but its the only one I could find with the right song.
Whip It!: These ending credits are just really fun to watch.