I've thought this long and hard.. but my opinions are not going to change.
So here are my top 2 lenses for a Nikon DX -body:
Tokina 11-16mm f/2.8 (older version without the focus motor)
There is just nothing better than this. Sharp at f/2.8, only gets sharper when stopped down. Focal lenght optimal for landscapes, night time star-photos, minimal distortion, built almost likeba tank, lightweight (no internal focus motor).. list goes on..
If you shoot landscapes, action photos, or pretty much anything where you might need a wide field of view, definitely get this lens. As a bonus, it's been said that this lens also works on FX-bodies at 16mm, but I havent had a chance to test this out.
Nikon 35mm f/1.8g DX
Optimal focal lenght on a DX body for pretty much anything (field of view equivalent of a 50mm on an FX body), fast aperture f/1.8 which gathers a lot of light, enabling you to use lower ISOs ( less grain ) and faster shutter speeds ( less camera shake ).
Pre-owned price around 100€ - 130€, buy it new for around 200€
If you are in need for a longer focal lenght, Tokina also has a 50-150mm f/2.8 lens, but I haven't had a chance to test this lens yet.