The best theme you'll ever use is one you make for yourself... My favorite theme is the modified FBL Dynamic I'm using. I converted all the scripts to lua, and shrunk the shortcut panel and hooked it in to a popup. It's my favorite, because I made it for me, and I like screwing with colors and fonts. :D

For other people's themes, I like technical stuff, where I can dig through rc files and maybe learn something. So Cerbie's stuff of course, plus fractal's (if only he'd make his scripts tidier!), and sryo's.