Blogs4Bauer.com (think that's the site) is running a "Death Poll" on their site. Consensus there is that it's President Palmer. I think it's Palmer and Tony. The Girlfriend thinks it's Chloe and Mike Novak.
I doubt it is Chloe, she has a good following, I doubt it is Palmer, Allstate wouldn't allow that. Might be the president character but I doubt that also. The current(as of last season) director of CTU since Sean Astin is going to replace him is a good candidate. The other one I am not sure.