My current acupuncturist recommended Lucky Vitamin and Life Extension to me. If I don't order from those places, I usually go to Whole Foods. I order some things from Da Vinci Labs. And my former acupuncturist was into Douglas Laboratories (he felt they were one of the most absorbable vitamins based on some book that is published in Canada that shows bioavailability of vitmains).
I third luckyvitamin.com. There website is easy to use. But if you do standard shipping expect it to take that long to get to you. Some websites I can pay for standard and expect it a couple days earlier than that...but not lucky.