Joe Lencioni , Nov 05, 2006; 06:38 p.m.
If you can get close (like on stage), I would recommend the 50mm f/1.4 or even the new 50mm f/1.2L if you have the money for it. Otherwise, I have had a lot of success with the 70-200mm f/2.8L IS. It's a great lens that will offer you a lot of versatility for being in the crowd. I have some concert photos on my website that were mostly taken with the 70-200mm f/2.8L IS if you want to have a look.