Just finished up a small 3.5'x3.5' Urban/CityFight board that I converted from an architectural model I picked up at a local auction.
Before:
After:
I blogged the whole process pretty thoroughly in a how-to post here:
http://chicagoskirmish.blogspot.com/2012/10/making-urban-wargaming-table.html
Nothing too groundbreaking technically, but -if I may self-promote a bit- there's some good methods for cheap and effective texture paint, fast sidewalks and spray-on road texture.