Seriously, unless they have really good dedicated lighting, then it's hard. I've shot at f/1.8 with high ISOs, and I use burst mode with shutter speeds at 1/10 or so. You'll be lucky if you get one out of ten. I'll post two shots tomorrow.
One was of David Allan Coe with good lighting, the other is a local band that had ambient bar light.
Also, when shooting at f/1.8, it's so hard to get what you want in focus unless you have a lens with USM or whatever fast focusing motor that the manufacture uses. f/1.8 is such a shallow DOF that you may focus on the face and if they shift a few inches while jamming and you'll have a shoulder in focus and nothing else. Short of using a flash, which sucks for concert photography, you just have to cut your losses and pick a better venue.
Edit: Motivation. If click the photo and go to the Flickr pages, you can view larger versions and see the difference. Both were at ISO 1600, but one had much better lighting letting me get a faster shutter speed and there for better exposure and less noise in properly exposed areas.
David Allan Coe with his lighting
Exif
Camera:Canon EOS 30D
Exposure:0.013 sec (1/80)
Aperture:f/2.8
Focal Length:50 mm
ISO Speed:1600
First try at shooting a band playing ever.
Exif
Camera:Canon EOS Digital Rebel XTi
Exposure:0.05 sec (1/20)
Aperture:f/1.8
Focal Length:50 mm
ISO Speed:1600
