The Tokina 12-24 F4 AT-X Pro DX is a fantastic lens for the $$. Hell it's just a fantastic lens (review here) period. Someone has one for sale in the Flea Market right now. I do architectural photography, and the Tokina 12-24 is my workhorse. Well built and tack sharp.
Thanks again, all! Neil, I saw those photos of Ireland and got all giddy. Thank you for sending me to the updated portion about the lens he used. I decided to go with the Nikkor 12-24 f/4. In the end, the little extra range, size, and ability to use filters (without handholding) won me over.