Back in March of 2006, I took a 9-month old Rory to Arizona to visit my mom and sister. I didn't want to bring Rory's birth certificate as proof of her existence, so I instead brought her to the DMV and got a child ID card for her. Fiona and I recently went to AZ to visit my mom and Roger, and I did the same for her (we strive for parity in the Mayhew household).
For $10, you get an ID card with your kid's funny face on it, and an amusing memory book item, to boot! Rory's picture is shown first; I think she looks like a drunken elf (about to tip off the chair). Fiona is busily waving at the photographer, who was flailing a toy around to keep her attention front and center.
The entire process takes about two hours, but what doesn't at the DMV? It is well worth the wait. Enjoy!