My parents' Rollei 35 camera - the only film camera I've ever seen that makes some compact digital cameras look chunky. With the lens barrel retracted, it's smaller than three 35mm film boxes, and even with the lens out the whole thing is smaller than the lens on my Nikon SLR.
A few hurdles to get over before I can give it a whirl, though. It has a fully coupled light meter, but this requires a type of battery that's stuffed full of Mercury and therefore now unavailable. Some websites sell a "zinc air cell" that should work. Also, the rewind is a little tricky - I ran some expired films through it this morning, and the first one was torn to shreds. I think I've got the hang of it now, though (fingers crossed).