Last month we started the monthly OWASP security blitz. We have a new month and a new topic. The blitz topic for May is Cross Site Scripting. There is also an OWASP wiki page were we're tracking the submitted stories, links, and more. The wiki page also has the topics for the next few months.
As a final note, I love one of the submissions from April on SQL injection - informative and funny!
-Michael Coates - @_mwc