Content-rich keynote presentations seem to be pretty rare, though they've improved some since the bubble faded. I was lucky last week to go to a conference (XML Europe) which had two excellent keynotes back to back, both exploring the synergy of open source and XML.
I've written both of them up for xmlhack. Jon Bosak explored how he hopes open standards and open source can work together, while Daniel Veillard examined how XML is used by open source projects. They were very different presentations, kind of like looking through opposite ends of a telescope, but they complemented each other beautifully.