Well it's so obvious Palps is sidious for reasons I know. But I found another reason. George Lucas was giving us hints that he is Sidious. Take TPM for an example. At the funeral pyre scene. When Mace and Yoda are talking about which was destroyed the master or the apprentice. Right after that scene it shows Palps just standing there, a zoomed in shot. You guys have probably already noticed this but I never have.