So you want an ultra-wide DX lens AND you want a fast f/2.8 aperture? Well, the Tokina 11-16mm is the one for you. It doesn't have a very wide zoom range, but it has a lot of positives: it's fast, very well-built, and it's very very sharp: probably the sharpest ultra-wide lens available for cameras with DX sensors. And you've probably got a zoom starting at 17mm or 18mm anyway; this is just for the really wide shots.
COMPATIBILITY NOTE (1): This is a DX lens. It will not deliver a full-frame image on a D3 series, D4, D600, D700 or D800 camera.
COMPATIBILITY NOTE (2): This is not an AF-S lens. It will not autofocus on the D40/D40x/D60, D3000 series or D5000 series cameras.