This pack contains every units and buildings as well as some trees and rocks that can be found in Age of Conquerors - and even some, marked BETA, that are not available in-game, as png images with transparency background.
I took the files in <a href="http://aok.heavengames.com/blacksmith/showfile.php?fileid=10923">All Bitmaps of all Units</a> and <a href="http://aok.heavengames.com/blacksmith/showfile.php?fileid=10888">All Bitmaps of all Buildings</a> and removed the pink/black backgrounds, substituting with real transparency. I did this with ImageMagick, and the commands and steps used are also included in a txt file.
Also, because of conversion to png, the total filesize is a bunch smaller than the original bitmaps.