IIRC fisheye lens are in the 15mm ballpark....
Fisheye lens actually causes that bowl/rounded effect...is that what you're after?
Or are you just interested in a good close up macro lens? (I think in Nikon speak it's called a Micro) which is a fixed focal length (no zoom/changing). A close up macro would generally be in the 15mm -18mm range.
I have an 18-20mm on my D90 and it does everything I need, I never have to change lenses, and I finally decided to sell all my prime lenses, and just use this one.