hey, i live in austin. Hope in the City is a good church with a solid young crowd. Austin Stone has a good young comminity too. EV Free does as well. Hyde Park Baptist used to, and I think they still do, but its been a while since I have been there.
I am no longer in Austin, but I spent most of my youth there. If you want to get out of the city I reccomend Main Street Baptist Church in Georgetown. www.msbchurch.com They have an excellent youth program that is growing well. I work with them when I am on leave, given the chance. I grew up with Anderson Mill Baptist Church in northwest Austin, but I cannot speak of their youth program, too many years abroad to know what they're doing now. Austin is a bizarre and wonderful place and I look forward to returning someday.