Ahem: fisheye? (although honestly, tilt-shifts are probably
the trickiest).

Panasonic DMC-G3. Rokinon 7.5mm f/3.5 UMC fisheye for micro four-thirds. No defishing in post--just placed the horizon in the center of the frame--otherwise, funhouse time:

G3. Rokinon 7.5 fisheye.
Horizon placement and use of foreground/background are key with the really wide glass. Also, objects may be closer than they appear through the viewfinder!

Because most of these very wide lenses have convex front elements and they go so wide, you may not be able to use a filter/hood to protect your lens. Exercise appropriate caution.