WordPress 2.3 is out. The feature getting the most attention (rightly so) is the new tagging system. The capabilities and features of the tagging system will grow as we see what plugin authors start doing with it. To support tags the database tables were changed (some removed, some added), so double check that you plugins don’t break when upgrading.
The new AtomPub code is in 2.3 as well along with update notifications for WordPress and plugins. Mark Jaquith has a great write up on his canonical URLs code.
Lots of good stuff, with more to come. Here is what is being talked about for WordPress 2.4, which should be out before the end of the year.