I've been shooting concerts for almost 15 years now. Started with an A2E and just got my 10D. Still experimenting with the 10D for optimum results, but I've found it to be a worthy successor to my older film body.
Since concert lighting is often times minimal and ever changing, I agree with the previous poster to get the fastest lens you can afford. I've been using a Canon 80-200mm f/2.8 for years and it's a fantastic lens. Since the 70-200 models are more current you may be able to pick up a good used 80-200, otherwise I've heard good things about, but not had any direct experience with, the Sigma 80-200 f/2.8.
With film I shot ISO 1600, which may be faster than what other people typically shoot shows with, but I can guarantee I was the only photographer with usable images when Neil Young decided to perform by candlelight. On the 10D I wouldn't drop the ISO below 800, but I'd be prepared to dial it up to 1600 if you're not getting shutter speeds at least equal to the focal length of the lens you're using. I haven't had much of an issue with noise, to be honest.
Since the environment changes so much with lighting and other stage effects, I most often shoot in auto program mode (I forget exactly what it's called, but it's the adjustment to the north of the green settings before you get to shutter and aperture priority).
As for a flash, you might be able to get away with using it for outdoor and/or daytime shoots as a fill, but for indoor concerts it's almost always a no-no. The EX series flashes will give you proper exposures if you meter off the right area (I always aim for the face).
Try to steady yourself against the stage if security and the surrounding envronment allow you to, that may help you steady your shots.
I don't have any of the 10D images on my web site yet, but if I could figure out how to post them in this message I would.
Hope that's helpful!
Seth