I can't speak for the others, but TED has HTML5 support and works great on my iPad.
Slideshare also has an iPad viewer.
EDIT: Also, blip.tv appears to work just fine.
Oh, good to know! Guess I don't need Flash on iPad for anything then.
Comedy Central, namely The Daily Show and Colbert Report
I'm just wanting hulu. Hulu+ is a joke.
TED talks, Slideshare, and blip.tv would have made far more compelling demos. Lots of good content trapped in Flash on those sites. Until they move to HTML5 I would use Flash on an iPad for those sites.