It's fair to say that Popes having...issues while in office is not a new thing. In fact current Pope Ratzinger doesn't come close to being the most controversial Pope, despite protecting paedophiles, clear anti-Semitism and continuing the Catholic Church's modern conquest to spread not religion, but AIDs. Even with these things he is still a progressive visionary compared to many of his predecessors. But that's only like saying someone's the least-obnoxious contestant on The Apprentice. It's not really a compliment.
For the list of '10 Worst Popes' follow this link: http://www.oddee.com/item_96537.aspx
Reading that list it's really hard to believe what went on. And impossible to judge who is the worst. The website decides Stephen IV is worst, but really, exhuming a body is a victimless crime. Benedict IX's behaviours are certainly surprising, but again, selling the Papacy is not that immoral compared to the others on the list. It's like lumping Bernie Madeoff and Stalin in the same category. Madeoff is bad, but ultimately his crimes were only financial. John XII is probably the worst in the list on religious grounds, due to the amount of sex he had, and I think worshipping pagan Gods and toasting the Devil are frowned upon in the Church. But don't quote me on that. However, Popes rejecting their own moral rules and having lots of sex while in power is actually quite common (http://en.wikipedia.org/wiki/List_of_sexually_active_popes, several have actually died during sex). In the list, I think Alexander VI's sexual morality was the worst. Fathering a child with his daughter is...well...needs no comment, nor does the whole orgy, naked boys in cakes thing. Urban IV and Innocent VI were also quite bad, with the amount of murder and torture they were responsible.
Thank God our morality doesn't come from religion, eh?