Earlier this week the Java SE team released the beta 2 for Java SE 6 (Mustang). Mark explains the JCP Technical Detail (this is formally a Maintenance Release of Java SE 5!). Danny has a general Introduction, including a link to a JavaLobby Discussion Thread on the inclusion of Derby. The download is here.
The best resource is a feature overview by Mark and Danny; check it out!
You can also check the formal announcement and title="On The Record - Java SE 6 Moves Forward">On The Record, Sun's official news blog.