Hey folks, there are alternatives to the Wishield...
One example (shamelessly blowing my own horn) can be found at http://arduinology.tumblr.com/
It provides an Arduino library for the WiFly series from Roving Networks. Sample includes a webserver.
It does work with the Sparkfun WiFly breakout board http://www.sparkfun.com/products/10050
, and should work with the updated RN174 available from suppliers such as Digikey.
If you can do surface-mount soldering, then you can save half the price and get the bare WiFly chip from Sparkfun for about $35.