I started using Emacs before there was any real support for themes so I just selected the default light configuration. I made a few tweaks like making the cursor a red bar but didn't do much fiddling otherwise. About three years ago, the white background started bothering my eyes so I changed it to
oldlace and I've been happy enough with the result that I haven't made any further changes.
Still, I occasionally run across a tweet or post praising some theme and I always take a look at the screen shots. So far, I haven't seen anything that I like more than my simple non-theme but I'll doubtless keep looking at themes people like and point out on the Web.
Now Yuriy Pitometsu over at the Google+ Emacs Community points to a very nice site that has screen shots and information on several themes. If you're new to Emacs or unhappy with your current theme, you should take a look. Each page of the site lists several themes along with a thumbnail screen shot so you can easily find themes that interest you. Clicking on a theme brings up a larger screen shot and more information. It's a very nice resource if you're in the market for a new theme. Recommended.