The two are Garden Grocer and We Go Shop. Both get very strong reviews (WGS had a spot of trouble a long time ago, but has been under new management for several years, and is back to providing excellent service for a while now.)
The model for each is slightly different. GG has a web site that you can browse and order from, and is probably a tad more expensive. WGS is less structured---you give them a list, and tell them which stores, and they shop for it. I happen to like GG's ordering model better, but others like WGS just as much.
All depends on how you want to do it. Can't go wrong with either.