Well, since there isn't a thread in the Texas regional forum, here's a couple places for ya...
Boutique Pets
Location: Garland Road, south of Buckner
Notes: Talk to a guy named Bill. Good fish selection, knowledgable people, but very impolite
Dallas North Aquarium
Location: Trinity Mills between Midway and Marsh
Notes: Very nice-looking place, excellent tank selection, decent live stock selection, mediocre prices, few knowledgable people, several people that don't know jack, very polite
Aquatic Designs
Location: Parker and Alma (in Plano)
Notes: Very nice people, most of them fairly knowledgable, very small place, poor tank selection, poor fish collection, does special orders, majority of their business is servicing tanks, excellent prices on live stock
Sorry if I should have waited to respond to the pending thread in the regional forum, but I was excited to see a fellow Dallasite into the hobby.