Here are the top five (5) resources regarding Google's latest major infrastructure update: Caffeine.
1) Help test some next-gen infrastructure @ Google's Official Webmaster Central Blog
2) More info on the Caffeine Update @ Matt Cutts' Blog
3) Video: Breaking News, Matt Cutts Explains Caffeine Update @ WebProNews (webpronews.com)
4) Google Caffeine: A Detailed Test of the New Google @ Mashable.com by Ben Parr
5) CompareGoogle.com - a neat little way of comparing SERPs between the current (live) version and Caffeine.
Have another to add to this list? Post it in a comment.