Get the Canon 50mm f/1.8 lens. It comes in under $100 (closer to $80, but others with a Canon setup can advise better). This lens will allow you to shoot so much better without a flash.
There are a few on this board who have it (I have the Nikon version for my Nikon set up) and have taken concert pics. I'm sure Kelly or a few of the others might have some sample photos.
This lens wont give you any zoom, but if you get close enough you'll be good to go. If you stick with a zoom lens that doesn't have a wide aperture, then you'll have to use ISO 1600 and have a pretty steady hand. If your more than 20 feet or so away the built in flash wont be as effective (the further away the less effective the flash will be).
There are others with more experience in this department, but that is my take.