I should learn more about design blog and twitter backgrounds. Really learn. Not just uploading a header image and changing colors. Here is a link to a tutorial for twitter. It's also best practices, so even if you are not a designer, there is helpful information.
Here are some fun designs (found here and here):
Hey, someone else is using this illustration from istockphoto.com. (See the referral card I designed for my hair stylist? Same flowers and animals...)
Do I have a twitter account? Yes. Do I tweet? Not really. But I will probably mess around with my background in case a client needs this service in the future.
Here are some blogs with unique backgrounds and graphics I like.