WordPress 2.9-beta-1 is available! Get it here: zip, tar.gz. Start hammering away.
You can also just install the super handy WordPress Beta Tester plugin to make the one-click upgrade feature upgrade you to WordPress 2.9 Beta 1.
Remember though — it’s still beta software, so backup your database and don’t run it on a site that you can’t afford to be buggy. 😉
EDIT: Here’s two links covering some of the new features, including my embeds feature. The Codex also has a list going although it seems to be missing embeds.