I just found this brilliant site called Bad Mags. As it says, it features cover art from different sorts of sleazy US magazines from the 1950s onwards. Crime, occult sex, skin flicks, gossips, bikers, rock'n'roll -- the seedy underside of America! Ungawa!
This links nice to FinnSleaze, my own cover gallery of (mostly) 1970s Finnish men's magazines. (Its mirrorsite has also a bit more images.)