The WordPress Theme of the Month for May 2009 is Gallery, released by Smashing Magazine and designed by Christopher Wallace.
Gallery is a very advanced WordPress theme for, well, creating image galleries. Based on the Thematic framework, it has integrated the BuySellAds Plugin, Contact Form 7, and WP-PostRatings. There are some nice jQuery effects throughout. The theme is, at the time of this writing, being used on MixCSS, another project of the designer.
The design is predominantly dark, which works well for a gallery. The background texture and navigation bar look nice, especially.