Austin Sketch Group: http://www.austinsketchgroup.com/
I'm not sure if these guys still meet up ever week up, but it's a great chance to hang out and draw with fellow Austin artists.
Austin Visual Arts Association: http://www.avaaonline.org/index.html
They hold excellent life drawing sessions, Sundays 2-5 and Mondays 7-10 p.m. , $5 per session. @ the AVAA building, 38th St. & Home Lane, 78705.