They will wirelessly upload pictures to your computer when within range.
The upscale version includes geo-tagging to tag your photos with the latitude / longitude location of the photo. The accuracy of the geo-tagging is questionable because it does not use actual GPS but a GPS lookup system from Skyhook wireless, and only works when within range of a wi-fi hotspot.
Prices range between 80$ and 130$ and should be available at retail locations or online.
More information about Eye-Fi is available here. Product information is available here.