Canon EF-S 17-55mm f/2.8 IS USM cheaper than 17-40L and better optically. Canon EF-S 10-22mm f/3.5-4.5 USM is one the same level optically as 17-40L if not better.
Keep also in mind that Canon 17-40L on crop is barely a wide-angle. Canon 10-22mm is ultimate for wide-angle with optical quality very close to Canon 17-55mm.
My 2 cents,
Nikita.
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