I'm not sure what kind of stuff you're looking for, ghost. 
You can call Jeff and take a drive out to his storage unit in Plano. I've bought quite a few records from him, I think rock, blues, jazz and soul, but it's been a couple of years since I last stopped by. His ad is here: 
http://dallas.craigslist.org/dal/emd/4829993243.html  I need to go see Jeff and check out what he's got lately.
E-Mart / Entertainmart at the corner of Preston Road & Alpha Road in North Dallas has a respectable used section, though the prices on new vinyl are too high. But I do buy a lot of used wax there.
Half Priced Books' flagship location on Northwest Highway just east of 75/Central Expressway is definitely worth a look with a large section of used vinyl, a lot of bulk 50 cent 45's, and they have great prices on those Spanish WaxTime jazz reissues if you're into those. I occasionally find a good OST there, and that's also where I will waste extra time flipping through all their 45s. That store receives all the 45s that didn't sell or couldn't fit at other stores, I think they told me 2,000-3,000 45's a month go through there.
I'd also go see Randy at Groove Net in Mesquite. 972-270-9898. Just call and make sure he will be there, he keeps weird/limited hours. Mon-Fri: 8am-4pm/Sat: 8am-2pm hours, but not always. And you wont' be able to find it either. But his selection is awesome, top notch, really a dangerous place where you can easily spend a ton on records you just "need" to have.
Josey Records at 635 and Josey is a huge store, not yet developed into whatever it will ultimately be, but there are a lot of used records of all varieties. I went on their soft opening weekend a few months ago and picked through all the OSTs but haven't been since.
Good Records on lower Greenville in Dallas is in a cool area with a lot of bars/restaurants. They carry almost all new vinyl, generally indie stuff but also will stock OSTs and imports.
There's also a place called Shake Rag on Live Oak that I've only read about. The news article says he has 500,000 records and loves rarities. Let me know if you end up checking it out. News story:  
http://www.dallasnews.com/entertainment ... ecords.ece
There's a bar + record store combo in Deep Ellum called Off The Record. We went a couple months back on a weekend night, it was pretty chill and not crowded, but they had good beers on tap. I didn't buy any records, but the selection was similar to what Good Records would carry. There was a variety/curio shop nearby in Deep Ellum, I can't remember the name, but the guy had a fair amount of vinyl in the back, and some of it was pretty good. I've been meaning to stop back by but don't make it down to Deep Ellum enough.
Anyway, have fun digging, enjoy Dallas. If you go to Deep Ellum go to Pecan Lodge for some BBQ.