Well, here we go then -- the Special Format Grids Package, or SFGPak for short.
The readme gives more information, but basically there's six (very simple) grids here (two of which are admittedly redundant with what's already been done), based primarily on 120 and APS film formats. The most interesting IMHO are the APS-P and 120 6x4.5 grids; the Holga grid probably won't be of much use to anyone, but it's there for people who like doing that sort of stuff in post.
They assume the 3x2 aspect ratio that the grid renderer is based on, and so look a little squashed on my A3000, but they're good enough to get the general shoot-and-protect idea across. (Incidentally, would it be possible to put in a feature request for roundrects in grid rendering? The Holga grid would look a lot better with them...)