O bar and Ghost bar are the newest trendiest places. If you're staying downtown, I would just stay around those.
Depending on how old\single you are, you might check out Duke's off 75 by SMU. There's also a ton of nice bars up the dallas tollway in Addison, again depending on your age\singleness. Check out the Sherlock's on 75 and the one on the Dallas Tollway in Addison.
Dallas also has the best gay dance club and best gay bars in the nation, near Oak Lawn and Cedar Springs, if you're into that.