Word is Episode 3 will hold a shocking revalation on the level of Vader's in ESB. I have looked for a possible cannidate. Obi-Wan and Yoda are out, as we know the direction that they take. Mace Windu would be shocking but not shocking enough. That left me with Amidala.
Let us consider a few things:
1) Amidala obviously seduces Anakin, she practically toys with him. Think sexy dress + raging fire. Seduction is a trait of the dark side.
2) She marries Anakin, knowing well that ths is an extreme violation and betryal of Jedi code, forcing Anakin into a life of deception. Deception is a trait of the dark side.
3) Remember Obi-Wan's words, "Never trust a senator." In a well written story this could be an excellent bit of foreshadowing.
4) In EP1 many moviegoers were bothered that the Jedi did not sense that Amidala was posing as one of her handmaidens. To quote Yoda, "Clouded, difficult to see the dark side is." She used deception (unseen to the Jedi), again, a trait of the dark side.
5) Remember in EP1 it was Amidala who put forth the motion that placed Palpatine in power.
6) Is it only coincidence that Palpatine was a senator from Naboo?
Many would argue that Leia remembers her mother, "She was very beautiful and sad." She remembers what she 'believed' to be her mother. Could be Bail Organa's wife or one of Amidala's handmaidens. Others would argue, "Sith, one master, one apprentice." Palpatine could make several apprentices believe that they each were the only one, being that they are not openly active.
Something to ponder...