What's the best Austin-area pet adoption service if I have to give away a dog with slight behavioral issues?

I have a relatively large Chesapeake Bay / Golden Retriever mix who was abused in the past, and therefore he's a bit wary around humans. Not at all beyond salvation, since a friend was able to gain his trust by herself, but he needs just a little bit of work. Due to unfortunate cirstances I have to give him away. Does anyone recommend a decent adoption service for an 8-month old large dog?