Thanks very much. A direct link to that lens is: http://www.amazon.com/gp/product/B00...SIN=B000EXP7Q0
From the sellers currently available (47st, Ace, Beach, and 17th), I'd go with Beach. 17th St is probably a better company, but they're not offering free shipping right now ($14 extra).
The Tokina 12-24 f/4 lens is an excellent lens, and many actually consider the Tokina to be superior to both the Canon and Nikkor lenses available in the same length and aperture.
This is a great option for wide-angled shots, on a digital "crop" body, such as the Canon 40D or even Canon Rebel cameras.
I would not suggest anything else, in this length. Sigma and Tamron options are wholly inferior, while the 10-16 f/2.8 Tokina is $200 more expensive with very little advantages.