Ask HN: Best technology related speakers?

Hi HN,

I am a member of a team within our student chapter of ACM, and we hold an annual conference in October. The conference is free to attend and we normally see around 600 attendees for around 16 or 17 speakers, a job fair for students, and a AI programming competition. This past year's speakers are listed here: http://www.acm.uiuc.edu/conference/2011/speakers.php

Anyways, I was wondering who, in your opinion, you guys consider to be some of the best speakers in the field, or even speakers you thought were surprisingly good after you saw their events. I want to start talking to people about attending, and I just wanted to get HN's opinion.

Thanks!