Random Gmail Theme

Gmail added 3 new themes to the gallery, but my favorite addition is an option that picks a random theme every day. If you can't decide which theme works best for you, select the "random" theme and Gmail will look different every morning.

Unfortunately, you can't skip the themes you don't like or at least pick a list of favorite themes.

A fresh mix: Gmail's Turf theme + Google Chrome's Grass theme

iGoogle has a similar theme sampler. "With this theme, you'll get to try out a new featured theme every day and decide whether you want to keep it."