Locally for costumes check out Electrique Boutique. Also Condom Sense on Greenvile (those two stores are very close to one another on Greenville). There's also another store, the name is escaping me at the moment, but they have locations on 75 @ Beltline and 635/Old Denton Drive. And the seasonal Halloween stores have a lot of to try on as well.
Most of these are going to have the same costumes from the same manufacturer in the same plastic bag. Good enough for a wearing or three, but not meant to really last beyond the tricking season.
Don't forget the upcoming Dallas Fetish Ball - two days of fun-filled, latex and leather clad vixen running around in a bar. Oops! Was that your bottom I pinched?