Courtesy of TFW2005.com, via The Allspark, here is some of the Concept Art & Prototypes that will be found in the latest edition of Generations 2011 - Volume 2:

Generation 1 Wheelie:





Generation 1 Fortress Maximus:









Generation 1 Overlord:





Generation 1 Pretenders:



Generation 1 Actionmasters:







Generation 1 Victory:



Generation 2:





Beast Wars - Optimi:



Beast Wars Neo and G1 Unicron:







MP10 Optimus Prime: