The thing that makes Webkinz differ from Beanie Babies, and makes them so hot among elementary school kids, is that the toy comes with a secret code, printed inside a tag which allows them to adopt their vitual pet. The tag must be removed and opened to get the code.
Once the tag is removed and the code is used, they become a consumable product and their valued decreases dramatically. For example, on July 16, 2007, a Webkinz Cheeky Dog with a new tag and unused code sold for $810. The same day, a Webkinz Cheeky Dog with its tag but with a used code, sold for $455 on Ebay. The retired Cheeky Dog is considered the highest valued Webkinz followed by the retired Cheeky Cat ($208), Puppy Love ($96), and Sherbet Bunny ($41). We anticipate that these value will increase quickly.
To give you an idea of how popular Webkinz are, check out the graph from Alexa beloq that shows the daily reach of Wekinz.com.