I use http://www.whcc.com
for my lab prints as they have one of the most flexible labs around (can accept files in both sRGB and Adobe RGB 1998 color space).
Their pricing is competitive on medium and large prints, but their small prints could be a little cheaper. They do photo and press printed products as well as canvas, velvet, and other fine art printing. They offer gallery quality prints and a variety of press products from business and comp cards, to coffee table albums.
If you need canvas prints, simplycanvas.com has the edge on quality (because they tweak every file for color before printing specifically on their system) and cheaper prices to boot.
You need to calibrate your monitor for WHCC and they have a system where you get test prints to make sure your system is calibrated and your color/density matches. They use kodak paper (which I'm not a huge fan of personally as I prefer fuji) but the results are unquestionably professional.
They will redo any of their mistakes at no cost and without question. they even cover items damaged in shipping.
They ship every order UPS ground for FREE. There is a $12 minimum order but that's never been a problem for me personally.
Hope that helps.