I'll swipe the YouTube clip from Allah, but point you there for the high-res QuickTime version.
At the risk of hatin' on a dead man, I'm not yet buying Ledger's interpretation of the Joker. There's some menace there, but where's the mirth?
Eh. Best Joker? Still Mark Hammil.
Oh... And if you dug Iron Man, in the works are Iron Man 2, Thor, Captain America, and then, yes... The Avengers.
The ultimate team-up. Sure, Batman and Superman would be a bigger team-up, but that's not going to happen.