Its quite a job figuring out who is playing, where.
I use VuenosAires, which is probably the best maintained site, but its still pretty hit or miss. It tends to cover the foreign bands the best.
My personal preference, when in Argentina, is to see Argentine music. I am less interested in 20 year old english or american bands.
To really keep up, I frequently scan the facebook pages of a bunch of bands I like, and see where they are playing, and who they like- which takes time and research.
There are a few reliable places, though, that I always check.
For instance-
Thelonius, which is an adult, jazz club, often has interesting acts on the edge of jazz, and almost always has good mainstream jazz.
Oreja Negra, in Palermo Soho, is a nice club that I check frequently, to see if I am interested in who is playing there.
Cafe Vinilo, just over Scalabrini from Soho, is another tasteful, adult place where you can sit at a table, have a drink, and see a band. Usually jazz and folk.
Niceto, on Niceto Vega, is the big rock club, lots of cumbia and electronic, too. Several bars, louder and crazier, but when the right band is there, I go.
CC Matienzo is the place the kids go- its cheap, and you only pay to go in the actual performance space- the other three floors, with two bars, food, and lots of little rooms to hang in, including art shows, are free. Its not expensive, and often there is an early show, at maybe 9 or 10, and then a main show that usually starts at 1 or later, and runs til 4 am minimum. Great, edgy, goofy bands play there, its quite the scene.
Sometimes, there is a little club called La Playita, on Federico LaCroze, near the station- its in a house, very intimate, usually acoustic cumbia, folk, and some jazz. cheap, cool, and hard to find, but only open in the summer, usually.
These are my main go-tos, but there are often pop up events all over town- again, it takes sleuthing to find em.