I remember him posting on his facebook discussion blog asking the fans what they'd like to see him work on next, and I was all like "Whaat? You mean you aren't already lining up new projects for when you're done with Heroes?" As much as I love him as Spock and Sylar, I want to see more of him in other fresh, new roles. He'd probably have to leave Trek for a while to make sure his take on Spock is still fresh and creative by the time the sequel is filmed. As far as Heroes, Sylar is the last thread that the show is hanging on for ratings. That sounds like a lot of pressure on Zach.
I'm super excited to see what he does in the meantime. Heck, I'd watch a B-grade romantic comedy if he was in it! He could turn that stuff into gold.