FWIW, I've purchased from Ammunitiondepot.com before, and would do it again. Their prices are pretty competitive on some things, an I like that they only list items that are in stock.
The downside, much the same as buying from other online sites, is that shipping is what kills the deal. I really wish these online sites would allow for slower, more affordable shipping. I think it would really help their sales volumes. To make it worth buying online, one has to order a considerable dollar amount, in order to offset the high shipping costs and make the entire purchase worth it...