I just stated using OSH Park recently and I'm very happy with them. I've already done about 7 orders.
You do need to order in groups of 3, so if you need exactly 10, have to buy 12. Also, they use a dark purple solder mask that's not going to suit everyone's tastes.
Aside from those things, it's a great prototyping or small run service. The turnaround is about 10 days for me here in Arizona.
If you use Eagle, you can upload your .brd files directly and it's very easy to use! The charge is simply $5 per square inch for 3 boards, and there are no additional costs. You get the boards shipped loose in a purple plastic bubble envelope.