I've been very satisfied with proflowers.com. They are available through the AA eshopping mall. I've been using them for years (before they were available for AA miles) and can't really complain. They have always delivered my orders ontime. They ship directly to the recipient via overnight FedEx, so as long as that is reliable in your area you should be OK.

I used to use 1800Flowers, but they screwed too many things up and I'll never go back to them.