http://www.nikonchat.com/nikkor-vs-nikon-2/

Nikkor 10-24mm vs. Tokina 11-16mm?
I need a new wide-angle lens for my Nikon D90 and I’m having a hard time choosing between these two. There’s a $200 difference between them (the Nikkor being more expensive).
Any opinions for image quality, speed, durability, etc? Thanks!
The Tokina 11-16mm is reckoned to be a pretty sharp lens & highly regarded. Better than many ‘brand’ lenses.
Another option (cheaper still, but tack sharp results) is the Sigma 10-20mm. Two versions a fixed max aperture of f3.5 and a slightly cheaper variable aperture version. Seeing as you rarely need wide apertures for landscape work, the variable aperture lens is fine.