ZT.art, a developer studio that has created a ton of themes for GO Launcher, GO SMS, and other GO apps. The themes range from subtle and colorful to aggressive and monotone. Some of the better ones include Eternally, Obsidian, and Fairy, all of which are free. In fact, most of the themes for both GO SMS and GO Launcher are free and there are dozens upon dozens to choose from.
Please note that you’ll need GO Launcher to use any of these Android themes!