New to Canon

I agree with many that have suggested the 24-105 f4L.  It's a sweet lens.  If you decide to get one, check out the ones being offered by authorized Canon dealers that also have eBay stores.  Often they sell the 24-105 in a white box, which was originally part of a kit that included that lens with a camera body.  Many are selling them brand new, still in the wrapper for around $850.  You can save $300 by getting one this way.  They include an invoice and a Canon USA/Canada warranty card.

Good luck

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