Pi Camera add-on lenses to make things go wide, REALLY wide, or really BIG.
The Pi by itself is pretty cool, but the REAL secret sauce is the high speed video port that the camera attaches to. Get a decent camera, and add a lens set to really make it impressive.
This isn't a standard lens set - this lets you really go wide, or go tiny, as it includes:
It not Nikkor-quality glass, but they're pretty good for the price!