I heard about this a few months back, but it's the first time I'm seeing a photo of it: an SD card that can transmit its contents by itself via Wi-Fi. Now isn't that cool?
Wired reports that the newest version is able to support RAW file images (used to be only jpeg files) and that it works with ad-hoc wifi networks, i.e. it can connect to your wifi-enabled PC, and not just a regular wifi router.
The Eye-Fi can also automatically geo-tag images. The Pro costs USD150. Still steep, but still cool.