Ive had two large prints printed from Adorama.com and have been very happy with them. The 2nd one was damaged during shipping (obvious UPS fault). I called Adorama just to let them know and they printed another and shipped it out immediately, I didn't have to mess with UPS. I was impressed with that.
Actually, I'd pick up one of any number of photography magazines and check their advertisers. A lot offer either free first prints or deeply discounted first prints. This way, you can send the same picture to several places and decide who you like best.
I went with Mpix and LOVED their service. Their Metallic prints with the luster coat are amazing... They bring your photos to life, plus the price is great and their shipping is outstanding.