Most reactionaries are going to immediately start crowning the Phillies due to the recent signing of Cliff Lee to a rotation that already includes Oswalt, Halladay and Hamels. However, one's long-term memory should remind them that the San Fransisco Giants outdueled both Cliff Lee and the Phillies last year when they captured the pennant.
The Giants will still have Tim Lincecum, who is arguably better than Halladay or Lee, as well as Johnathan Sanchez and Matt Cain, and almost their entire lineup back from last season. They still have Brian Wilson in the bullpen. The Phillies still do not have a great closer in Brad Lidge and lost Jayson Werth to free agency.
In the playoffs last year, most people had the Phillies favored then too, but the Giants came through with big bats and out hit them. The series with the Phillies only went six games, even if Lee can get another win, which is in question based on his WS performance, the Giants still would've beaten them. The Phillies have done little to improve a line up that struggled to hit-well consistently last year, Cliff Lee won't change that.
I do think this makes the Phillies the largest contender to the Giants, but until someone else wins the 2011 World Series, the San Francisco Giants are still the defending champions.
Overall, just a word a caution, don't rely on the reactionaries and let only your short-term memory fail you.