I see this question being asked a lot these days especially when people are pre-ordering Diablo 3 by the thousands.
The real answer is that no, Diablo 3 will not have any Pre Order bonus of any kind.
Pre Order bonuses are usually tied to specified stores or to pre orders in general and are put in place to trick people into securing a copy of the product. Blizzard is not known to do this and they certainly aren't going to do so with Diablo 3. The only bonus you get is the face that you are ensuring you get the copy on release date :).
If you want the closest thing to a Diablo 3 Pre Order Bonus, consider getting the collector's edition which comes with a lot of goodies, as shown in our Diablo 3 Release Date article.