Earlier quoted context omitted.
I've had good success with the NXP LPC178x series. Cortex M3 with onboard Flash and SRAM. Ethernet is onboard and easy to attach with a simple PHY, also works well with extenral SDRAM and expanded Flash.
yeah I also used that a while ago, but I don't think I can fit an ethernet client for Robotic Operating System on it. Doesn't appear straight forward anyway:- http://mbed.org/forum/bugs-suggestions/topic/2662/?page=1#co... Hmm, that Xport product is £50 from mouser. Not bad
The other option is something like the TI CC3000, a serially driven wifi module. Adafruit just launched a cheap breakout module.