Aaaah don't make me choose Red Hot Chili Peppers, Alkaline Trio, Jenny Lewis, Yeah Yeah Yeahs, Gogol Bordello, Handsome Furs! All freaking fab!
If I had had had to choose, Karen O from the Yeah Yeah Yeahs is my best pick, hands down. She just has so much smurfing energy, she is constantly dancing and squirming around. Brian Chase is so damn good about keeping rhythm for the crowd and Nick Zinner is great striking his chords between songs just at the right time to give the crowd a little taste of his skills. Their entire show is just one acid trip.
Ah, second might be Nate Ruess from fun. His presence on stage is just unlike anything I've ever seen before. He's magnificent.
Honorable mention to Panic! at the Disco. Brendon Urie just sat there and banter with the crowd like he was having a one-on one conversation with you between songs, it was fantastic.
One of my favorite live performances I've discovered on YouTube, though, goes to The Black Belles and their song Honky Tonk Horror. I just love love love this version, and there is such a clear influence of the White Stripes in their music. Love it.