Bulk Reef Supply is good as well, but more so for cal, alk and mag than for salt. And between Drs F&S and Live Aquaria (which they own) the service is exceptional.
I generally try to stay local with salt because of the weight. Shipping charges are often bumped up because of it. Try asking your LFS if they can get the type of salt you're looking for if they don't carry it. Most have access to more than what's on their shelves.