Here is a list created by the city of Austin that contains every music festival that happens in a normal year. There are simply too many to put on this page, but the highlights include South by SouthWest, the Austin City Limits Music Festival and the Austin Reggae Festival. There is a festival at least once a month and some months have up to 5 different events. There is even a rodeo event coupled with a music festival in which the riders spend the day performing and then trade off with music artists in the evening.
They really do have a music festival for as many genres as you can think of!