Could a USB wifi dongle be used as an Arduino Wifi module?
If you have a regular Ethernet shield for your arduino (with RJ45), you can turn it into wifi with a wifi adapter such as the Netgear WNCE2001. I did it and it works fine. I am able to make my arduino send data to by android tablet via a wifi access point. I am now struggling a bit to implement a peer-to-peer wifi connection from the arduino to the tablet without the external wifi access point in order to take it into my car, but I think this is achievable as well.