Couple of links to some "interesting" visual themes.
This site is called DeviantArt. It's like a site where a bunch of people submit their own artworks and stuff, make friends, and comment/collect artworks. There's all types of artworks and I searched Visual Themes in the search bar so:
No membership is require to view submissions, but I think you need to be a member to post, comment or collect. I'm a member.
Themes for computers; you can download them. Seems more like wallpapers to me but . . . oh well, I may be wrong:
This site is called Agrapha. The link leads to its porfolio page. It says you will find Agrapha's 'professional' stuff. The web designs section could be seen as visual themes for web sites I guess:
It also talks about what to do in making these sort of stuff like about details, colors and etc.
This is from crystalxp.net and this image is just the same (sort of) design and visual theme but in 4 different colors: http://www.crystalxp.net/galerie/img/img-visual-styles-4-vista-shellstyle-for-xp-sagorpirbd-9465.jpg
StudioTwentyEight's visual styles have some really cool looking ones. And they are up for download (and purchase) : http://www.studiotwentyeight.com/visualstyles.htm
All I got.