Check out the Tamron 17-50mm F2.8. It should be around USD350 (or at least was when I got it), and it's a really great lens for the money. If it was weather and moisture sealed it would be perfect, but you do get what you pay for. The lens also got quite good online reviews (photozone.de, fredmiranda etc.). If you need to see some test images, you can check photozone.de's reviews, or my phototracker - every photo in my photo tracker with a focal lenght in between 17-50mm was taken with the Tamron.
If you are start looking for something even wider later on, I'd recommend the Tokina 11-16mm F2.8 over the Sigma 10-20mm F4-5.6, although both of them are not in the USD350 range.
Good luck!