A bunch more videos are posted at the Confreaks MWRC 2008 page. I’ve seen a number of people saying good things about them.
I think Jim Wierich’s Shaving with Occam was a pretty amazing talk. I’ve already past it around work, and am hearing good things from even the non-rubyists. I think it says a lot about the Ruby community that Jim was able to pull off a keynote that didn’t have any Ruby in it—Lisp, Forth, and Erlang all got some time on screen though.
I don’t think you’d go wrong with any of the talks though. Go spend some time in the archive. Once you finish the 2008 MWRC videos, you might turn your eye to some of the other archives as well.