Check out the Austin Bicycling Association - they have group rides every weekend. I think the website is www.austinbicyclingassociation.org - but its been a while. If you join you also have access to their maps. I'm a big fan of riding out in the country between Georgetown and Round Rock. My sponsor 360 Cycleworks does a no drop shop ride every Sunday. We always have a team member riding sweep to make sure everyone is doing ok and knows the route. It starts from behind the shop at 8:30 Sunday mornings.