I have added a pair of books, and replaced a duplicate entry with a different book on the Unity 3D Book Round-up. Another two Unity 4 books have been announced with release dates in March of 2013.
The first newish entry is Essential 3D Game Programming which replaced the duplicate entry of Unity 3.x Scripting on the list ( thanks for the heads up in comments! ). This book has been on my radar for some time but had minimal information, now there is a bit more available. That said, something about this book is really setting off my warning alarms… starting with the fact the artist on the cover graphic doesn’t match the author of the book. Caveat emptor and all of that!
The other two are from established publishers, so no concern in that regard, both are upcoming books on Unity 4.
The first is Learn Unity 4 for iOS Game Development published by APress.
The second is Unity 4.x Cookbook published by Packt Press. Oddly enough, this book isn’t yet up on Amazon. Will edit the links when this changes.
As stated earlier, both of these books ( as well as Beginning 3D Game Development with Unity 4 all ship in March of 2013.