The view from Lou Neff Point at sunset
There are a few good spots to view the skyline of Austin from, and one of my favorites is Lou Neff Point in Zilker Park. Skylines are one of my favorite subjects, especially when there is a river in front of it (Austin of course, but also Nashville, NYC and more). I actively seek these out when I travel.
Anyway, Lou Neff Point is easy to get to. Just Google it and depending on the time of year, you can nearly drive right to it. During our big music festivals, most of Zilker Park is closed to cars so you end up with a much long walk. Either way though, it's well worth it for the view!
And if you are looking for more things to shoot in Austin, I have compiled a list of all the major stuff. Take a look, and if you are coming in for SXSW and have enough free time, I also have this available as an eBook should you be interested in that. Enjoy!