what do you tip a barber?!
Depends- where you get the cut. In a trendy location a bit more than a regular barber shop. Also depends on whether or not you like the cut and appreciate the work they did on you.
Figure about 10-15% the cost of the cut.
According to the Original Tipping Page, generally 15% of the cost with a minimum of $1. If you don't get your hair cut too often, then $5 would be appropriate.
Of course, this is if you get your hair cut at a barber shop. If you get your hair "styled" at a beauty salon, see the second link for additional information.