The Jmaa El Fna square is a UNESCO heritage site, largely due to the story tellers that pass on stories in Arabic, but also note the musicians and various other stalls. However, be prepared to pay a small tip of 5-10Dir whenever taking pictures/videos of their performances.
These interesting performers are most commonly spotted at night. During the day, look out for the snake charmers (dare you not prepare a tip when the other side has a cobra at its beck and call?!) and the delicious orange juice stalls!
The Berbers are one of the major ethnic groups in Morocco. We had one evening of Berber music at the villa, which was just great. The style reminded me very much of music I've heard from Mali. Someday, in my next life, I'm going to be an ethnomusicographer.
This is a nice Video about a Marrakchi traditional music Group :
Marrakech Traditional Music