The Tokina 11-16mm f/2.8 AT-X is the best ultrawide zoom available for Nikon DX cameras, better than even Nikon's more expensive 12-24mm AF-S DX.
If you want an ultrawide zoom for your Nikon DX DSLR, this is my top suggestion as of 2008. (For the D40, D40x or D60, you still need the Nikkor 12-24mm for autofocus, and for Canon, I'd get the excellent Canon 10-22mm.)
This Tokina 11-16mm is the world's fastest and sharpest ultrawide lens for small format digital cameras (Nikon DX and Canon 1.6x). Considering its bargain price of under $600, its the world's best ultrawide lens for digital SLRs.
It is very well made. Its distortion is much easier to correct than the Nikkor's.
If you haven't actually shot with these lenses, you'd think this Tokina competes with Nikon's 12-24mm f/4, Canon's 10-22mm f/3.5-4.5, Sigma's 10-20mm f/4-5.6, Tamron's 11-18mm f/4.5-5.6 and Tokina's own 12-24mm f/4. (Tamron announced work on a 10-24mm f/3.5-4.5, in January 2008, but it doesn't exist.) I compared all of the older lenses back in 2005 in my Digital Wide Zoom Comparison.
Having shot all these, there isn't any real competition for Nikon cameras. This 11-16mm is superior, even to Nikon's own lens, and this Tokina is one of the least expensive. Feel free to read the other 95% of this review, however the details below only are interesting to 5% of my readers.