The wonderful ASPCA has a mobile adoption van that goes into different areas to encourage adoption within the five boroughs of New York City. I think this is a wonderful idea. Sadly, this is only in the New York City area but at least it's happening.
From their site:
All of our animals are spayed or neutered, up-to-date on vaccinations, microchipped, and come with a leash or carrier, as well as a certificate for free follow-up veterinary care at the ASPCA Bergh Memorial Animal Hospital. Adoption fees range from $75 to $200. Our knowledgeable adoption counselors are on hand to provide all the information you need and help you find the purrfect match.
For more information about our Mobile Adoption schedule, please call (212) 876-7700 ext. 4120.