My monitor isn't calibrated. I like to take stuff to Sam's Club, because they're cheap, and the quality is pretty good. i've been finding that when I print big, 16x20+, if my original is contrasty, they come out real dark.
A custom lab near my house doesn't have that problem. I tell them to print from my original, and not to correct, and the prints come out just about exactly as I see them on my screen.
Not sure why the big difference, but I'm guessing it's the quality of the printers they use.
If you're interested in trying them out, everything can be done online, and they ship, so you can use them anywhere in the country. Prices are fairly competitive as well.
www.myphotopipe.com