The printing providers that I use

I mostly use these two places for my prints: They color correct my images to make them work with their printers' color space.

http://www.mpix.com/

http://www.bayphoto.com/

Occasionally I might print at Costco, but just prints that are not important, mostly I use them for the convenience of having the prints within the hour.
Costco, or any other pharmacy style machine do not color correct your prints, so they will look just ok, either dark or without much detail in some areas.

http://www.mpix.com/

http://www.bayphoto.com/