http://www.fudzilla.com/news/mobile/37464-m3-computer-claims-to-be-the-world-s-smallest
Excerpt: Researchers at the University of Michigan have developed a computer, which is said to be smaller than a grain of rice. Dubbed Michigan Micro Mote (M^3), the tiny fully autonomous computer measures as small as two millimeters across.
The tiny M^3 is capable of taking pictures, reading temperatures and recording pressure readings. Researchers plan to implement it in several applications ranging from medical to industrial purposes. The tiny size also allows users to inject it into a body, wherein it will be capable of performing ECGs and take pressure and temperature readings. The oil industry is also said to be interested in the Mote. It can be inserted into oil wells to help detect oil pockets.