There are several posted in the Styles section here and at UBBDev, simply look for threads I created in these forums for the ones I made. You can see some of these over at
Elite Web Gamers (the anouncements forum has links to the preview url for each of the themes I have created; however, not all of these are freely distributed).
My UGN Security forum is for all intensive purposes stock in reguards to the styles. Keep in mind that the stylesheets are ONLY the colors/graphics of the overall outlook; without having a way to allow users to switch templates on the fly there will be no actual themes as template changes would effect a "theme".