On my D200 I usually shoot with the Nikkor 24-70 f/2.8 G lens. The equivalent in Canon is (I believe) the EF 24-70mm f/2.8L USM.
If it's even half as good as the Nikon equivalent then this is a great general purpose lens. Not good for wildlife but great for landscapes and portrait. But it is around $2,000. The only real downside is a lens like this isn't really made for the lightweight body of a EOS 450D/500D.
Have you considered the EOS 50D? This is a slightly better build than the 450/500 bodies.
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