First Alleged Botcon Classics Thundercracker Images
Please keep in mind that this could be custom work, an early version of a real toy, or any number of other things besides a final legitimate toy. That having been said, there is a poster on the ACToys message board who claims to have a Classics Thundercracker (recently announced as an upcoming Botcon convention exclusive). You can view the images at this link.
UPDATE: After some initial discussion, it seems pretty definite that this is a hand-painted custom. Still, it's a nice attempt and food for thought for those trying to imagine what the actual toy will look like.
You can discuss this in this ongoing thread. Thanks to Seibertron for the link.