A brief look at some of the more colorful Popes throughout history:
Sources: The Rotten Library, Wikipedia, and The Catholic Encyclopedia.
Pope John XII (937 - 964)
Had sex with pretty much anything that moved. Killed off people that got in his way. Finally was himself killed by a dude who came home and found him humping his wife.
Pope Benedict IX (1012 - roughly 1065)
What happens when a horny, spoiled 12 year old becomes Pope.
"The stories about Benedict's behavior reached heights comparable to the most notorious popes. He was accused of habitual sodomy and bestiality, and was said to have sponsored orgies where any available orifice was considered fair game. His excesses were so legendary that they helped prompt St. Peter Damian, a cloistered monk, to write an extended treatise against sex in general, and homosexuality in particular, with a special focus on how these practices had become rampant within the Catholic priesthood and even the papacy itself... Damian recorded that Benedict "feasted on immorality" and that he was "a demon from hell in the disguise of a priest." Although Damian singled out Benedict for particular scorn, the diatribe was directed at the clergy in general. Benedict's sex life might have been colorful, but it wasn't exactly unusual...
Pope Stephen VI (? - 942)
Talk about holding a grudge.
After becoming the Pope, Stephen VI had his predecessor, Pope Formosus, put on trial. The fact that Formosus had been dead for about seven months didn't bother him much.
He ordered the rotting corpse dug out of its grave, draped in papal attire, put on trial and found guilty. He had the dead pope stripped of his papal title, had the three "blessing" fingers of the right hand broken off, and buried in a pauper's grave. Then not long after that he had the poor corpse dug up yet again and then thrown into the Tiber river, where a monk later recovered it and restored it to the original tomb.
After Stephen VI himself was deposed, imprisoned and killed, Pope Sergius III after him (who earlier attended the posthumous trial of Formosus) upheld the trial and had Stephen VI glorified for it. There are conflicting accounts that he ordered the corpse exhumed yet again and beheaded.
Rotten Library article on Pope Stephen VI
Wikipedia article on Pope Stephen VI
Wikipedia article on "The Cadaver Synod," or the trial of dead Pope Formosus.
Sources and further reading:
ETA: There are so many more Popes to highlight, but I honesly didn't have the time to bother. Check out the links and stuff for moar. Enjoy :)