You might want to check out my blog article on equipment for shooting concerts:
Marc Sabatella: Concert Photography - Equipment
In it, I show images shot mostly from pretty close up using a variety of different focal length, which should help you get a sense of what they look like. But really, I'd recommend shooting with a cheap (too slow to be useful) zoom first to *really* understand the focal lengths that work for you, before committing any serious money to a lens that may or may not end up fitting your own style.
Me, I shoot from pretty close and like what are essentially portraits with instrument. 100mm is kind of the sweet spot for me; anything a little wider or a little longer would do as well. So if I were to go with a zoom, the 50-135 is the obvious choice. Others prefer a wider view; others shoot from farther away and need longer lenses to get the same basic framing I get with a 100 or 135 at most.