My friends Rashmi Sihni & Jonathan Boutelle recently released a really cool product, slideshare.
Simple idea. Think youtube for presentations. Upload a PPT or PDF, it converts it to individual slides that can be bookmarked, linked to from a blog, tagged, commented on, etc. Cracks open presentations so they can be searched and really makes it easy to find.
You can see one of my talks here:
Hopefully they will support keynote in the future as well as some ways to handle animations/transitions. But even without this it's a great place to find recent talks.