Until now you had to wait until you died to even to be considered for a stamp. Stamps.com has a new service called PhotoStamps that allows you to upload a digital photo and create a postage stamp of any occasion or "special person" in your life. 4-6 days later, you'll get your personalized stamps in the mail.
This service is not from the USPS, so it's not really an official stamp. But, they say the service complies with all USPS laws and regulation and that you can use these stamps just like the ones you get at the post office. Pretty neat idea...though the price ($16.99 for 20 stamps) is enough to keep me using this for anything but a one-time experiment.