Depends what you are interested in. Ottobar, Metro, and Soundstage have lots of punk, metal, indie rock, hip-hop, and dance nights. Creative Alliance has a wider range of performances from international artists to more specific cultural celebrations. Union Craft is a brewery and only does the occasional concert, but they also do family oriented events.

If you want to stay in the loop you can use the Tumblr I run (https://baltshowplace.tumblr.com/) that lists most of the concerts happening in town each month. I also have an Instagram (@baltshowplace) that keeps people up to date on any changes to shows and low ticket warnings.