I have purchased several items from Optics Planet, and they are very good to deal with. Their prices are often discounted, they actually have the stuff they advertise in stock most of the time, and their shipping is reasonably priced and speedy.
I've ordered Blackhawk Serpa mag carriers from them, and other Serpa parts (drop-loops and a holster) and they were helpful on the phone, and quick to deliver.
Blackhawk is also VERY helpful on the phone and ships relatively quickly.
Smith and Alexander is a company that should be on the "bookmarks" list of EVERYONE who owns a Para Ordnance--they are one of the ONLY places that sells aftermarket parts for the Para double-stacks. They are VERY friendly on the phone, and quick to ship.