Austin City Limits Festival
This article in the Austin American Statesman gives a nice rundown of the situation.
They lowered the number of tickets available this year from 75K to 65K so it won't be so crowded. The tickets are going for $105 for a 3 day pass at this point but according to the Statesman article they expect to sell out in either June or July. So buy your tickets now and mark down the date:
September 23-25, 2005 - Zilker Park - Austin, TX