I think if that's the amount of money you want to spend, and you want a lens that tries to be an all arounder, that's a pretty nice option. You always make tradeoffs somewhere with glass, so if you're comfortable with the shortcomings associated with that style of lens, I'm sure you'll be quite happy with it. Check out
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I'd say forget the T2i, the 40d is a great camera despite it's age. At this level, the differences between Canon and Nikon are mostly in the interface, neither will take better pictures than the other. So I'd suggest going to a camera shop and playing with a bunch of dSLRs from both companies. Even if you can't find the exact one you're considering buying, you can get an idea for how each company approaches ergonomics. Most people I've spoken to find one really natural, and the other really annoying, but there's no telling who will like which.