There is no affordable super wide-angle lens for Nikon DX but this one:
Variously sold in other locales under the brand name Samyang, Falcon, Bower, and Rokinon. On Nikon’s APS-C sensors, it throws a frame-filling image with a 180° diagonal viewing angle.
As a fisheye lens, of course it doesn’t depict in a rectilinear fashion. That effect is fun to use sometimes, but gets old quite fast.
There is software to “defish” fisheye images, I used the Fisheye-Hemi™ Plug-In for this self-portrait at my place of work to get from here:
And what is the image quality of the Walimex fisheye lens like?
Well, it certainly isn’t a Distagon in the corners, and image space manipulations as mentioned above stretch information in the corners even further. I think it will be ok for nature shots, but wouldn’t even think of photographing architecture with it with any aspirations of correctly depicting a building. If it was purely for the “Wow!” effect, well, that’ll be worth an occasional try.
I especially liked working with this lens in crowds like in the lead image. The Fisheye-Hemi™ Plug-In is specialized for these situations and bends the verticals straight again, but not the horizontals. If one wanted a rectilinear image made from fisheye RAWs, one would use the PT-Lens plugin. It takes a much smaller crop out of the original field of view and leads to odd eggheads at the borders of the image.