A post over at Wowhead brought Firefox Personas to my attention. Once you have the Personas addon installed, new themes are super easy to use: the Personas menu gives you a bunch of starter personas, including "new," "popular" and by category (with a randomizer). All the personas are previewed live as you scroll through the menus, which is the real killer feature here. Even the mouseovers on the Personas site skin your browser in real time.
Here's a small sample of personas. I usually hide some toolbars for Firefox screenshots, but personas tend to look better with a larger canvas.
[gallery link="file" columns="4"]