You can't just discount Orton's 5 INT game against the Bengals. My vote would not be for him. I don't think we're even sure right now that he's going to be the starting QB come the end of the season.
If the vote were right now, I'd have a tough time deciding between Caddy, Brown, and Heath. But with Caddy's pain, and Ricky's carries, I'm guessing Heath Miller will be ROY come the end of the season.
I think there's also a chance some WR will have a huge 2nd half and steal the honors... someone like Brandon Jones, Braylon Edwards, or Chris Henry. Maybe even Matt Jones.
As for defensive ROY, I really like Odell Thurman, but I don't think he gets the award. At least 3 of his 4 INTs (actually all 4 I believe) were off deflected passes that he just happened to be in the perfect (lucky) spot to grab. He has missed numerous key assignments - ask Heath Miller about that TD catch against the Bengals. And on top of all that, LBs without tons of sacks tend to get overlooked in voting.