Apparently, San Francisco Cardinal William Levada is one of the most influential people involved in the selection of the next pope, according to the Washington Post and others. Levada actually took over as head of the Vatican’s doctrine-guarding office after its former head, Cardinal Joseph Ratzinger, was named Pope. This will be Levada's first conclave as a new Cardinal, having previously been archbishop of San Francisco, and he's been pretty vocal about what he's looking for in a new pope.
He's a tiny bit more gay-friendly than his current successor, Salvatore Cordileone, having publicly made the distinction between pedophile priests and those who might be homosexual. He said, "By nature homosexuality is a not a predatory activity, it is a sexual activity that the Catholic church does not condone."
Though Levada and others doubt that an American cardinal will be in serious contention for the job of Pope, the main possibility would be the charismatic Timothy Dolan of New York.
"I don’t know what the Las Vegas oddsmakers are saying today, but I don’t think it’s likely that we would see an American pope. It would be an additional complexity for an American pope to have to deal with the perception that some of his decisions might be perceived to be dictated by American governmental policy ... Probably I will tend toward looking for a younger man [than Benedict] who still has better energies, at least for a while, to really to be able to give himself completely to this."
Many cardinals have indicated already that they are looking for another charismatic leader like John Paul II, rather than a stodgy oldster like Ratzinger, who, it was assumed, was only going to be a guardian of the church doctrine for a brief time.