These five are my favorites, and also the ones I think are the best, although I base this on no objective criteria.
The CW used this in a Gossip Girl promo, it got stuck in my head, and I've been listening to it ever since.
4. I'm a Slave 4 U
The trick with this one is not to listen to any of the lyrics (they're pretty stupid).
3. Oops! I Did It Again
A classic! Remember when Jack taught Grace this dance on Will and Grace?
2. Til the World Ends
Newer isn't always better. But in this case, it is. Note this is taking place on the last day of the Mayan calendar: Dec. 21, 2012.
You've gotta love the red wig and the diamond body suit.
P.S. My infatuation with "Toxic" has nothing to do with this video, I assure you. Obsessed as I am with Christian Bale, I liked the song years before I knew anyone used it in this fan video: