Ramachandaran's talk had a profound effect on me (neuroscience/brain). Mark Bittman's talk was great, but I like everything that man writes (food). Clinton's talk made me feel like I knew him better after watching it. It felt very personal. Dave Eggers' talk was beautiful (learning). Ze Frank's talk was good if you follow his stuff. Murray Gell-Mann gave a beautiful talk (physics). I bought Dan Gilbert's book after watching his. Alan Kay was, obviously, very good. Sir Ken Robinson's talk was absolutely great also (learning.)

This is just a small sample of the ones that I have seen and liked. I haven't seen most yet.