Are you in business with a sales tax ID and all? Then I LOVE H&H & Pounds , Finao (albums)... MpixPro, Millers
If you are not in business then there are quite a few who will still sell professional prints:
Mpix.com
BayPhoto
AdoramaPix
WHCC
CPQ
and about a million others.
I think I see most new people go with WHCC and really love them
In still in the middle of getting everything set up, I'm working on wordspress and my website, I signed up with millers, but I was also looking into bayphoto.
What country are you in? I would assume you are in the US because that seems to be where everyone on the internet is from!
I can recommend two Pro Labs in the UK but they're no use if you're wanting the prints in the US. They ship to the US but it's expensive enough within the UK!
Don't know where you are located. I'm in virginia and I use bullock professional in Albemarle, NC. I upload everything and have it back within two days and they are extremely accurate. They also provide excellent customer service and inexpensive webhosting. They are about 2 hours from where I live. I have been very pleased.
I've never been dissapointed in Richard Photo Lab, but than again, I shoot film, and have never had them print anything big before..but if their print quality is anything like what they do for film, than I have no doubt that they're stellar
just keep in mind... that if you use a good lab, you will need to make sure what you are sending is what you want. Use a good calibrated monitor and submit images with the correct color profile.