Ah, the cottered crank. Imagine with me: at one point, this was the pinnacle of technology. Crank arms falling off was kind of like getting a flat tire or sweating out your tweed, it just happened. We happen to have a modest selection of these ancient artifacts occupying a bin in our parts room. Nothing combines billows of nostalgia with a cold sweat of terror like an old Dunelt or Robin Hood 3-speed rolling in the door with a seized cotter pin in the crank arm. In fact, when bike mechanics tell horror stories around the campfire or prank-call other bike shops, the subject is often cottered cranks.
We are waiting to see if Trek will make a BB90-compatible spindle for a cottered crank setup, but suspect that Cannondale will beat them to it with their BB30 design.
Here are a couple of gems from the mine: a 3-pin Stronglight (good luck finding chainrings); a 5-pin Nervar with a 50mm BCD (can fit chainrings from 26t up to 52t if you can find them!); and a microscopic Sugino, probably for a unicycle.