Compur leaf shutters---the 50s Compur-Rapids in a TLR, or an early rimset---but I don't have the onomatopoeic vocabulary to spell the sound they make. At the end of the day I don't think I ever really heard a leaf shutter I didn't like, but the Compur mechanics have something unique.

At the other extreme, I'm lately very taken with the enormous flapping, crashing noise of the Optika 6x9 SLR. It's such a steampunk beast of a camera in the first place that it seems totally consistent for it to make a noise like metal-shop class at a school for goblins.