I've used a number of different online retailers including:
liveaquaria.com
saltwaterfish.com
gatewayaquatics.com
mrcoral.com
aqua-escape.com
I've been happy with all their products, but there are some ebay sellers like zoafrags and reef empire that seem to have superior livestock at great prices. I'm trying to find something like that but in an online retailer.
Thanks for all the suggestions so far, all that I haven't seen yet are getting added to the bookmarks. Problem is, with the high cost of shipping, I really need to find everything I'm looking for in one or two places.