Here are some sites I found really useful during my search for property in Austin:

http://www.texasdavid.com
- Tons of free resources on this site, MLS listings, Cash flow calculator

http://recenter.tamu.edu
- Lots of information on Texas real estate, quarterly "Tierra Grande" magazine is very useful

http://www.statesman.com/business/content/business/realestate/index.html
- Listings, trends, and the Neighborhood Profile section is very helpful for investors who are not from Austin