Greg's links to all PDC videos and presentation slides is very useful...
http://coolthingoftheday.blogspot.com/2008/10/pdc2008-quick-video-link-list.html
I prefer all links as presented on Greg's page rather than having to navigate through the heavyweight AJAX pages of the Microsoftpdc.com site to find videos and slides: https://sessions.microsoftpdc.com/public/timeline.aspx
Update: 10 Nov 2008
If you can't find a PDC video, perhaps it has not yet been published, follow this feed to find out newly published PDC08 videos http://channel9.msdn.com/posts/pdc2008/RSS/