Two NEW, COOL and FREE BlackBerry themes popped up at mobile.blackberry.com last week. The Surreal and Stargazer themes can be found in the Themes section under Fun & Games.
The downside - availability of the themes is dependent on the device model and OS version you are rocking (Curve & 8800 Series users (not on 4.5 betas) should be able to get both). For details, help and more information on these new themes, visit this thread in the CrackBerry forums. Enjoy!