I print and sell my work through deviantArt, and I must say, I'm reaaally content with their print quality. They get a lot of the revenue, but the quality is fine
Since they do all their print preparation themselves, you have to submit RGB files anyhow. I colour calibrated my CRT monitor, and the prints look pretty much like what I see here, so it's all good with me.
Haven't tried local printers yet, as their prices are so steep, that even with shipping from america I'm still cheaper with dA. And I know what I get...
I couldn't order things like a canvas print or so, though, shipping that would just be beyond reasonable