I had the same predicament. I bought the EFS-17-55 IS USM (2.8) and i love it.
I was actually debating between the 24-70Land the above. The 17-55 is my day to day lens and the glass is L quality. The only downside is , of course incompatability if ever you consider going FF. I started with a XSI back in August and i just purchased a 50D.
The 17-55 perform very well.
Canon get you on this one though as you have to purchase a hood ($40.00 in Canada!)
Hood is standard on the 24-70.
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