6. Caligula
Partly financed by Penthouse publisher Bob Guccione, the 1979 historical epic about the Roman emperor Caligula's rise to and fall from power has probably more kudos in its credits alone than all of the other films on this list put together. Gore Vidal wrote the original screenplay (but demanded to have his name taken from the title once he'd seen it) and it features performances from Helen Mirren, Malcolm McDowell and John Gielgud, but none of them were able to save the hyper-sexual and ultraviolent mess Guccione and principal director Tinto Brass had created. Infamous for being crass and vulgar in its depiction of sex (both unsimulated and fake) and horrific violence, Caligula has left a bad taste in the mouths of more or less every critic who's seen it, but that didn't stop the film from having an incredibly profitable run. That's possibly due to the draw from the hardcore porn segments filmed by Guccione and inserted willy-nilly into the movie with little regard for plot or continuity. But 35 years later people are still talking about the film, and it seems like every other day a new or alternate cut of the film is released. It's a disgusting curiosity, if only because you're not likely to find many other pornos with Helen Mirren and John Gielgud starring.