I'm a fan of Half Price Books. The North Lamar location is decent for fiction in Spanish because of the proximity to the university. All of the locations are great for general fiction in English.
Book People is a good place to buy new releases and the classics. But I always have trouble finding anything "out of the ordinary" there.
Looks like half-priced takes the prize, it's hard to beat!
The only other semi-unique bookstore I can think of is "Brave New Books", which has a large selection of conspiracy-type books, and a small selection of historical books.
But I know there have to be other bookstores here in town that should be of interest, anyone have anything else to share?
I like supporting BookWoman. It can be a bit pricey, but it is nice to support locals!