Most bars don't really advertise...Just go on yelp and type in "gay bars". That should do the trick for anyone unfamiliar with the area their in. I think whether or not there is a large straight crowd just depends on the night and the location. I live in Madison, WI, which is a big college town, so the bars nearer to campus are going to have more straight people, especially straight women. Other locations in less hip parts of town not so much.