If you're doing landscape, want a zoom, and 28mm is often good enough for you, I suggest:
Tamron 17-35mm 2.8-4 Di LD SP.
It's under 1000 bucks, has low dispersion, and the sharpness rivals L Quality glass. This site has a very favourable review of it, as well as here:http://www.photozone.de/8Reviews/lenses/ta...nikon/index.htm
I have it in Canon mount for my 30D, and it's an excellent lens. The optical quality is very high, and the build quality is also pretty good. It's a full frame lens, so on 1.6x it translates roughly into 27-56, which is just wide enough on the wide angle to cover what you usually use, but also has the potential to be used on a later, full-frame model.