T-Mobile has a deal with Skinit where you can make a custom skin for your G1. I did it, it was about $23 shipped. http://www.tmobileskins.com/
Quality is not bad, on 3M material that is supposed to not leave any residue if removed. I was disappointed in the back cover portion as it was much smaller than I anticipated. The pieces for the front were fine.
Not sure it was worth the money, but still a neat way to personalize your phone.