Those of you who attend JavaOne will know Josh Bloch, Neal Gafter and Bill Pugh's series of highly entertaining Java Puzzlers. Now, for the first time, one of these talks is available to people who are not JavaOne attendees: Josh and Bill gave this year's Java Puzzlers talk at Google.
I wouldn't dare spoil the fun by posting any of the puzzlers or their solutions (although Josh blows the surprise on one of them). This is definitely worth the time of anyone who does any programming in Java (and has 1 hour and 14 minutes to kill).
I would be remiss if I didn't point out the Java puzzlers web site, where a book is available.