The 24-70 f/2.8 L is not a very good value on a crop body, because most of the money goes into paying for the part of the image circle that you're not using (because you're not full frame). A lens like the 70-200 f/2.8 L, on the other hand, gives you the full bang for the buck. I'm sure you've already considered lenses like the 85mm f/1.8, 100mm f/2, 135mm f/2, and 200mm f/2.8.