Just this afternoon I was looking up the wifi module Async use.
Its the Microchip zg2100mmc
Its available in the UK for £18.38 +vat.
The external antenna version is available as well for the same price
I think RS components have them listed as well.
It needs 3.3v and a breakout board unless you created your own board.
Does the schematic show level shifers as well?
But Im sure you could use the Wishield libraries once you have it hooked up.
Gordon
Looks like just a Wifi module by itself sells for about $50:
Obviously Wifi could be cheaper, since you can get a USB WiFi adaptor under $20:
http://www.amazon.com/TRENDnet-54Mbps-Wireless-Adapter-TEW-424UB/dp/B000636JD8/ref=pd_cp_e_3
but that may depend on PC host processing for doing the protocol... The trick is how to hack that into an Arduino compatible system. If you figure it out, let us know!
Gordon - good info on the chip!
I want to figure this out. I am not necessarily trying to manufacture/proto anything, just tech toys. Think of the possibilities...
Yes, the drivers for the USB wifi adapter do the heavy lifting. Don't get me wrong, Async has created the 85-90% solution, the rest is getting the price down.
Its all horses for courses.
The unit that Async use requires the tcp/ip stack to be on the microcontroller and is relatively cheap at £18.00 or so. and the stack is already built in to available libraries that you can copy from async.
The sparkfun unit has all of the TCP/IP stack onboard and you communicate via serial so all singing and dancing solution requiring very little on the microcontroller. And costs a little bit more.
again you should be able to use the sparkfun libraries for the wifly shield.
A USB based wifi solution may cost very little but a microcontroller could not implement the neccesary drivers.
Also the drivers will be proprietry and probably only available for windows. I doubt that they could be reverse engineered for the Arduino in any form.
Another solution would be an ethernet shield stacked on the arduino plugged into a cheap wifi router.
Ethernet shields are fairly cheap.
Thats going to cost more than the ZG2100 solution and more bulky hardware.
So as far as Ive worked out the cheapest solution for the Arduino would be the ZG2100 built on a prototype shield or custom Arduino board. At £18.00 plus a little bit for the other compnents I think that its a very cheap solution.
No PC in the middle or wifi router plugged in to the Arduino.
I think Ill have a go sometime to expand on my Arduino compatible board.
http://scratchpad.thisandthose.org/scratchpad/article.php?story=20100715160140327
I think it would work out cheaper than the blackwidow to build for myself.
Gordon
The pics are great! Your rig is awesome! The detail you have investigated thus far is inspiring. I am going to try on my uno, but ultimately I want to implement on the ModernDevice BBB (if possible). Custom proto board for sure. Thanks for your input! I will feedback my findings when I finally get a chance to play. First I need to order a ZG2100. If they gouge on shipping, that could sink the ship.
Very nice! 
Recently I am playing with the Asynclabs WiShield 2.0, everything works great. I need a raw TCP client socket code (just like the one with Ethernet shield) to send and receive data unlike the HTTP GET/POST which comes by default with the shield. I really appreciate if some one can point me in right direction.
@jvincent
Have a read through the examples with the library.
And the Async labs forum.
There are examples you can follow.
Gordon