Command Decision: Test of Battle, you don't need to buy this one. Though I'm sure I will at some point to support em.
This one takes out the Test of Battle section (actually - as soon as I posted the pic at the right, I noticed it says TOB still...what gives? I'll have to look into this.) the Scenarios, and many of the data charts. They did update it with the little errata that exists and a few clarifications. They did this to lessen the cost of the book and for printing it.
The cool thing, they're including some of the charts and extras that came in the book on their site - though I don't think they're up yet. They must still be recovering from Historicon. (btw maybe next year for the big H?)