I don't know much about public schools, but I've heard that the Austin Waldorf School is pretty good. If you have girls, there's also The Girls' School. Another really, really good one is KIPP Austin, but I'm not sure what the reqs are for that. It's a charter school in East Austin, and stands for Knowledge is Power Program. It was started by a couple of Rafe Esquith's students...he was on PBS a while back for teaching Shakespeare to 4th graders. Oh yeah, and there's also The Griffin School. I bet a few school ratings searches could help you decide. I taught music at a K-12 private Christian school, which is why I sort of have an idea about these schools. My husband was hired by and almost taught at KIPP --- he just had a much better offer with a tech co. He said "I would have cried" if I had seen their music students; they were that disciplined.
I've heard good things about Mariposa Montessori for your little one, but I'm afraid I'm not much more helpful than that.
Good luck to you! I know a lot is restricted by where you live and tuition. Hopefully this was somewhat helpful!