Dave has linked to some good karaoke sites. Are there any others that you know of that is should visit.
For buying CD+G discs I usually visit these two sites first.
Pocket Songs and Session
I visit Pocket Songs because so many of their discs have guide vocals on them. As a singing teacher these are really useful. I like Session because the service is good and I like their extensive search engine.
So which sites do YOU use and why?
CC
