tm - I currently use a Nikon D300 or D70 body with an 18-200 f4/5.6 if the event is well lit and I want maximum flexibility when the distance from me to subject will vary significantly or a 70-200 f2.8 for stuff like yesterday at Carver where it's a bit darker once you factor in the shutter speed, ISO, etc. I have also used an 50mm f1.8 in the past as well for dance competition when it was very dark. For those, I simply cropped in a bit closer afterward but that was mainly because it was the only lens I happened to have with me at the time.
