IMO Fish Paradise in Ft Worth is probably the best store in Ft Worth. Fish, drygoods, LR, LS (1.99 #) and quite a few softie frags (although he recently went up $5 on the frags). You can usually find a good deal there. Decent prices!
The Aquarium & Much More is mostly FW with some SW. Can sometimes find a good deal there.
The Fish Place has decent prices, but unless they have made some changes since the last time I've been, they're water quality and tank upkeep could be a lot better. Don't get me wrong though, I have purchase clarki clowns from them. One didn't make it, but I called and they were happy to give me another, I just never made it back. I also got LR from from them.
Keller Farms, very small SW area and their R/O water melted my Xenia!
Tranquil scape in Arlington. I only went in when they were first opened, but they seemed kinda pricey. Not much of a selection at the time, but again, they were just opening.
Pet Village in Duncan has a selection of SW fish and they're prices are decent too. Also have drygoods and FW.
Saltwater Paradise is also the storefront for Extreme Corals. If you're going there vistit their online store if you sign up for their emil list you $25 off your first purchase. Huge selection of corals, usually a good deal to be had. Some SW fish in store, but the corals a better buy.
DNA is what everyone else said! It is a huge store and they have everything. They've got a bigger inventory of fish than I've seen anywhere. You will pay a premium though. I have seen fish in their tanks with what I thought was ich, but I'm no expert. I will say that I've purchased most of my fish from them though. Haven't had any problems.
Aquarium Trading Company is pretty big too, selection not as good as DNA. Pricing is comparable to DNA maybe a better buy here or there. Could do better with their tank upkeep though. Though I haven't been in a couple of months. I've gotten R/O water from em (.30/gal).
All the LFS I mentioned are on Marc's LFS list on his site. Most are in Ft Worth, since I used to live there, but now that I've moved to the Colony I mostly go to DNA. HTH