This is one of the places to go that has good, live music on most nights, done by local artists before they get too popular and start doing mega venues like O2. It's a pretty regular venue of this sort in Zizkov, and one of the better places of the neighborhood.
If you're tired of the touristic jazz music and want to see the real local styles of Prague, then Slušnej Kanál is a good bet. They host the local bands and musicians before they get big enough to pull the super crowds at O2.
Be sure that you check to see if someone is playing on their webpage.
Su: 16:00-00:00
Mon-Th: 16:00-02:00
Fr-Sa: 16:00-03:00