I remember the first time I saw someone get their head faux-lopped off by a guillotine. Some cheesy old movie where a lady's head plopped into a basket. I was way too young to see something like that, and was pretty stunned (and probably scarred for life). Despite all that, I've always enjoyed seeing a guillotine replica in a haunt - almost always with a smear of blood on the blade and a stuffed dummy missing a cranium.
Here's a guy that makes minature guillotines with amazing levels of detail. Neat site with a photographic history of the guillotine with some pretty graphic images (just a warning).
Here's an old-school pic from flickr. Love it.