You could consider getting a fast f2.8 constant aperture lens, such as the Canon 17-55 f2.8 IS, Sigma 18-50mm f2.8 or Tamron 17-50mm f2.8.
I personally have the Sigma and it is excellent, great range on a 1.6 crop body (although you may find it a bit short if you are used to a 17-70?) and allows me to take indoor shots without flash.