How much should you tip a hair dresser that does a rockin' job?

I've had the same stylist for the last 10+ years, and I always went with my Mom who took care of tipping... now I'm on my own, going to a new place with a new person... and since I'm confident that she'll do a great job, I want to know ahead of time how much I should tip.

Thanks in advance! :o)

any thoughts? (0)����������������