Check out the FAQ - but lemme tell you a little bit about my experiences with concert photography.
99% of the time you either can't, or SHOULDN'T use a flash. This means that your lenses have to be at the very most, f/2.8. You're probably going to have to bump your ISO to at least 800, probably 1600, depending on the lighting setup. Since grain is easier to fix than motion blur, I'd suggest going overkill on the ISO just go insure that all of your shots are at least in focus.
Depending on the concerts you're going to, getting close to the stage will either be:
2) not easy
If 1, then you really shouldn't need anything more than a 35-85mm.
If 2, then you will probably need an 85.
If 3, then you may need a really expensive lens - like the 70-200 f/2.8
The question is, are you willing to spend the money to buy a camera / lenses to get great shots? Do you want to be paid? Or is this just something for fun while you're at the concert? Do you have a photography background, or do you just love music? If you're just doing it for fun, I'm sure your current camera will do you just fine... but if you want to get some really kick *** shots that people will want to pay for, you're either going to have to become a god at using your current camera - or get another one.
I want to be remembered for the
people I helped make memorable;
personal success is overrated if it
doesn't help everyone's progress.