LiveAquaria is always great. Good prices, very reliable and great customer service. I've ordered from them a few times and never been disappointed.
I also recently ordered from Vivid Aquariums. My package arrived today, though I won't see it until I get home from work. I'm not as happy with them as I am with LA though. I placed my order two weeks ago, and am just now getting it. When you place an order with them, you have to wait 1 to 4 days for them to call/email you to setup a delivery date. Or in my case, nearly two weeks, and even then one of the fish I wanted was sick, so they couldn't ship it. Though I do like that they didn't want to ship a sick fish.
Both vendors have a guarantee on most livestock. LA is 14 days, Vivid is 15. I know that LA gives you credit/refunds with very little hassle if something dies. No need to show them a pic of the dead specimen, or ship it to them with a water sample or anything. I don't know how Vivid Aquariums handles it.