In early 2010 I implanted an RFID transponder in my right hand, in an attempt to motivate my self to work on a certain hardware project.
The tag itself is a Phillips HITAG-S 2048, packaged in a 2mm-diameter glass capsule. This is not exactly bleeding-edge technology, but it does include a "secure" challenge-response authentication mechanism and a few kilobits of programmable memory, making it somewhat more interesting than the common read-only ID tags.
Below is a short video showing the USB RFID reader reading the tag's UID value. Currently I can only reliably read the tag through the back of my hand, although with some tweaks to the coil and the decoding routines it would probably be quite possible to read the tag palm-down.