I was just at the fish gallery the other day and the plant selection wasn't horrible. It wasn't great either, it was just the basic, run-of-the-mill plants you see everywhere else. However, the prices did seem a bit cheaper, especially compared to Dallas North Aquarium. Cherry Shrimp at DNA were $6 bucks whereas they were $3 ea at Fish gallery and even cheaper if you bought a lot of them. The tetra selection isn't very great at Fish Gallery, but it seems to have a lot of saltwater and cichlids.
If you are looking for rummy-nose tetras every, hit up Exotic Aquatics in Plano. They're the only place so far that I've seen that has a ton of them in shop, and the price isn't horrible I think. The selection there isn't amazing by any means, but for a small shop it is pretty good and the quality of the fish is great. They are really well cared for.
Another place worth checking out is ABC Tropical on Greenville up in the Richardson area. It isn't that great for general tanks and the like, but if you are looking for something unusual they have a lot of interesting fish. They got a few arrowanas and some of the bigger types of catfish. They also have a good selection of South American cichlids, especially some different types of flowerheads. However, if you are looking for discus this is DEFINITELY the place to go. The discus selection is unbelievable, and I don't think I'd be stretching it if I said this is more than likely one of the premier discus breeders in the country. He has amazing discus, ranging from huge to small. He has a whole back section of the shop that is private that is devoted to breeding discus. So basically if you are looking for discus hit up ABC Tropical. The selection is just unbelievable.