Ladyada has a PCB Cost Comparison Calculator that shows the significant differences in price between various low volume PCB vendors, but what’s missing from the chart is the answer to: What vendors are people actually using?
If the cheapest fab house is also the best, obviously the more expensive vendors wouldn’t be around, would they? Unfortunately, it’s usually not that simple, cheap usually means slow, or low quality, or both.
I know that some visitors to this site make prototype PCBs at home and others send them out to be fabricated. How do you get your prototype boards made? Vote below.