Also, worth considering with the D7000 is the ability to use older "D" lenses, as the camera has an in-built motor for focussing. I am not sure if Canons are the same. If your on a budget it's worth considering some of the older D lenses, I have had the Nikon 28-105, 24-50, 28-85 & 75-300 and I must say all theses lenses have performed excellent, as they were originally designed for full frame. Also, they usually run around the f3.5-4.5 aperture mark so not's so far behind the F2.8 lenses.
The 28-105 is a classic lens with a great following, for a reason. You can pick these up for circa £100 -120, the 75-300 around the same and the other lenses around the £50.00 mark. It's worth considering if your on a budget.