LA Reefs - Specializing in Live Coral, Macroalgae, and Inverts for Reef Aquariums
is good, as is liveaquaria.com, whom I have ordered from. Everything arrived healthy and on time.
My absolute best experience ordering aquarium flora online was from Gulf Coast Ecosystems (www.live-plants.com
). Excellent selection, though most varieties are seasonally available. I orered their "Halimeda Sampler Pack" (which would be better named Calcareous Green Algae Sampler Pack) with an emailed request to not get any Halimeda since I already had some. The pack is supposed to include 5 plants. I got 3 shaving brush, 2 mermaid's fan, 1 pine cone, and about a half dozen small C. Barbatos. Quality was superb, quantity was well above what I paid for. Strongly recommend them!