At Least NINE New Characters in OotPBooks
As many may remember, when Jim Dale read Goblet of Fire, he had claimed to have done 125 different voices. Well, in the recent Wall Street Journal article he says he's done 134. In fact, his Web site has recently been updated to mention the same as well.
So what? Well if you think about it, that means there will be at least 9 new characters in Order of the Phoenix compared to Goblet of Fire. And some of Dale's voices from GoF were specific to attendees of the Quidditch World Cup so there may be a few more. Check out The Lexicon for a full list of GoF characters.
(Kudos to reader Michael Smith getting this before me)