Yakface has found a new variation involving the sculpt of the Super Battle Droid. There is a catch to this variation however, you have to open the figure to be 100% certain of which one you have. If you are a carded collector though, Yakface believes that they have found a way to tell without actually opening the figure.
Heres the news from their website:

The first version has a chest plate which is totally flat. The second version has molded circuits and gears which are raised slightly. The difference is very noticible as you can see from pictures below the difference is very noticible.

Now, the good news. It does not appear that this is a "hidden" variation which requires opening the figure to see which version you have. (Although I strongly encourage freeing figures from their plastic prisons as soon as possible.) The flat chest figures are in the earliest releases of the Super Battle Droids. They appear, based on my unscientific study of opening a lot of carded SBDs, to be only in those figures which have background scenes and the "corrected" sticker on the back showing the battle damage.