If you don't plan on moving to a full-frame camera in the near future, I'd recommend getting the 17-55mm f/2.8 IS. It's the best general purpose lens for an APS-C camera. It would be good for landscapes, street life, studio, and portraits (at least on the long end). For dance events specifically, you'll likely want something longer like the 135mm f/2. The 135mm f/2 would also make a good portrait lens, too.