I think that the ""Sunshine Retail"" (appropriately named) is a great second hand shop! I especially appreciate its mission, namely to raise money to help the poor of Houston. I discovered this by chance while chatting with one of the volunteers. They are part of CCSC (Christian Community Service Center).
At any rate, I found everyone quite friendly and helpful. I also found some terrific deals, although I admit, I did have to wade through a lot of racks. You won't find much in high end designer clothes, but you will find nice mid range labels for sure.