I've been to the larger Half-Priced bookstores in Dallas, and those are very good. But they do not compare to Recycled Books. Nothing in the area does.
Three warehouse-sized, well-organized floors of books where you're likely to find nearly anything. They also sell CDs and DVDs. And the prices are excellent.
Warning: If you go to this bookstore, have a little time to burn. You may find yourself wandering the aisles for hours.