I use ExpressPCB a lot. If you use their ProtoPro service you get 4 boards of up to 21sqin, double sided, coated, tinned and with silkscreen for $179. You can put as much stuff on those boards as you want.
I make circular boards up to 4.5" diameter by silkscreening a circle on the board as a cutting guide for later. Works fine.
They also have much lower cost options, such as bare copper with no silkscreen. You get good product fast from them. They will only accept board layouts submitted over the internet, made using their software. Their software is OK, but lacks design rules checks and other niceties. You *can* link a schematic to the layout so that ti will show you where traces have to go. How you get them there is up to you. It won't tell you if traces are overlapping or too close together. And it won't do a rats nest layout automatically. They will not accept Gerbers made from other vendors software, which sort of sucks since i have software that WILL do all those things
For fast prototypes they are very hard to beat.