I use three services.
1) AP Circuits in Canada. These guys are awesome. They have barebones prototype which is without solder mask, but with plated through holes... then they have Proto Plus which has silkscreen and soldermask. They quote, IIRC, 3-4 days for Proto Plus, but if I order before noon Monday, the boards ship Wednesday. Most of my boards are small, I think for a 1-inch square (2.5cm square) board, it's about $25 for two with the Proto Plus service. Very high quality boards too. Shipping to me is $25 and I get them the next day. I probably do 1-2 orders a week with these guys, they are as reliable as a rock.
2) Myro. Very good quality, price is pretty decent, although I would not expect them to be all that competitive with guys like PCB Cart for 10 unit orders. But if you are at 50-100+, they are very good. Plus a full featured online tool to quote which even does stuff like fiducials, panelization, aluminum core, 2oz+ copper weights, ENIG/HASL, etc, and lets you choose your solder mask and silkscreen colors. Their prices have risen over the past couple years though.
3) Ultimate PCB. Lower priced than Myro, but not by a ton. But excellent quality (in Canada) and they have EE's on staff who will add services at no charge like panelization and such if you need it.
Also check out PCB Cart.