I would also like to get something more common. Getting the Wiz550io is like $17 for the module itself and $40 for shipping. eBay is full of W5100 Arduino shields under $10 (free international shipping).
Do you think the w5100 would work with some of the tweaking mentioned above? Or is there any fundamental problem? From what I can see is that the w5500 has double the internal buffer and number of channels. Something I could live with wrt features.
Any hints welcome!