I'd be surprised if it's Clark, Warnock, Freedman or Robinson.
Clark and Robinson are both testing the lower leagues as young managers and are doing very very well. Why would they leave their respected clubs for a sinking ship? Warnock won't come because it's well publicised that Bates is tighter than a duck's arse. Freedman has build a very talented young squad who just got knocked out of the Carling Cup on penalties, literally seconds from Wembley, plus it's the club he loves.
Personally I think someone along the lines of Gordon Strachan or Gary McAllister, people with strong associations with your club would be more likely to take up the role. However Bates could go for one of his Chelsea mates and pinch Di Matteo.
It remains to be seen who the next manager will be, but what wasn't forseen was Grayson's departure which reeks of panic sacking to me.