If black and white aren't enough for you, ColorWare is now offering their gadget coloring service for the iPhone 3G. Their iPhone site allows you to customize parts of your phone with 35 different colors on an à la carte basis. Obviously you have to send in your iPhone and the service takes about two weeks.
Unfortunately, it's not cheap. Just to color the back of the phone is $150 (all prices are US dollars), with additional color options for the frame, home button, SIM tray, earbuds, and dock running $10-$20 each. In fact, if you went wild and purchased full customization, your bill would be $230 -- more than the iPhone 3G. On the other hand, can you really put a price on being the only guy whose lilac-colored iPhone has a Candy Apple button?