OmniVision OV6920 CMOS would be the way to go. It's the world's first 1/18-inch camera sensor, and is therefore the world's smallest camera -- almost as thin as a Samsung phone. The camera is designed to work as part of a pill which can be swallowed and flow through your digestive system, or for firing from a rather large syringe. Did we mention our no-injecting-cameras policy? We happen to be rather strict adherents.
[Via The Raw Feed]