Recommended PCB houses / Assemblers
I've used Advanced Circuits (www.4pcb.com) before (located in Colorado).  They have a pretty good special I've used a lot.  4 layer boards for $66 each (qty 4+).  They also have a FreeDFM service that checks your gerbers for errors.

They also do assembly, but I've found that assembly costs are sometimes more expensive than the board itself.  If you're doing this for a hobby, I've heard of folks using toaster ovens for SMD parts.