I'm going to echo my answer from this questionthis question. If you've got no power or space limitations, you can just buy a WiFi router that can run Linux, and pull out some of its IO pins to do whatever you want (they've got at least a UART and some GPIO). I'm pretty sure you still can't get a microcontroller + WiFi module for less than a prepackaged WRT54GL, which has all the bugs worked out, and a metric pile more CPU power than you're going to get from a PIC or Arduino.