The 2nd Street District stretches from Colorado Street to San Antonio Street.  It features a lot of restaurants and high end shopping (local and a few chains). It's a great little walkable area that sits at the heart of the city just a short distance from some of the city's best hotels. One of the highlights of the area is Moody Theatre, which is home to Austin City Limits Live.

Tip: Parking in this area can be a challenge. If you can find parking along the street or nearby streets- this is your cheapest option.  Otherwise, use this list of parking garages.  Some of the options do allow free parking with restaurant or store validation.