I like 16:9 a lot, some cameras I only ever shoot in that setting, just to exercise my brain, and to try and keep a look with the files from the same camera.
I sometimes shoot in abandoned buildings, and I always shoot that in 16:9, probably trying to convince myself it lends a more filmic feel.
I even like the panorama masks that some 90s film cameras had. of course they're a gimmick, but they can give an interesting look.
I'd like to experiment with the anamorphic lens technique, or the ratios that Rob has posted, but I think not being able to see the finished product through a viewfinder or on a screen would cause me too many problems.