Looking for a wide angle lens

I am looking for a wide angle lens for my 10D. I am considering the Sigma
15-30, the Sigma 12-24, the Tamron 11-18 due out later this year, the Tokina
12-24 due out soon and possibly the Canon 17-40. What I have decided that I
really need is 24-28mm on the wide end and a reasonably sharp lens in the
$500 range +/- $100. The Canon 17-40 is appealing (and pretty expensive) but
I know that there will be times when I would like to have the 35mm
equivalent of a 24mm lens. I have also considered just getting a 15mm lens.
This lens primary use will be as a travel lens and 28mm equivalent on the
wide end is a requirement.

From my research, including viewing photos taken by the Tokina, I think I
have it eliminated. I have had compatibility problems with Sigmas in the
past, but beyond that I have had good experience with the optical quality of
the EX lenses. It's not perfect, but they are generally a bargain.

I guess what I ask is for any experiences, good or bad, with any of the
mentioned lenses that would make you choose any one over the others if you
had my budget.

TIA

--
Eric Miller
millereric at bellsouth dot net

Convictions are more dangerous enemies of truth than lies. - Freidrich
Neitsche