McBride's usually has a good selection of used guns, and a bin of used leather to pick from. Their prices tend to be on the high side, and they usually don't budge much, if any, from their posted prices.
My favorite place is Tex Guns in South Austin. It's a family owned and family run gun store crammed into a tiny little place. The owner, Chuck, is very knowledgeable, and friendly. If you don't see what you're looking for, ask as he has stuff stashed away in little corners and crevices. Be sure to look at the display cases carefully - he has quite a few interesting pieces in there and you can easily overlook something if you just do a quick glance. Chuck's prices are usually very competitive (i.e. reasonable), and he's usually willing to work with you on the price.
Red's actually has two locations in Austin - one north (in Pfluegerville), and one south. He usually has a few guns in the used section. The prices are fair, but there doesn't seem to be any flexibility in the pricing. Both stores also contain indoor shooting ranges, so it can get pretty crowded and noisy at times.
If you get a chance, stop by the Salt Lick in Dripping Springs, TX - the best dang BBQ in Texas.
Best of luck,
Dave