concept mech by lingy-0.deviantart.com on @deviantART
Oz the Great and Powerful - Steambots by michaelkutsche on deviantART
References for various fundamental things - composition, balance of details etc. I don't have sources for most of these as its something that was lying on my hdd for a while, but you should be able to look it up through google images.
Stranski Character 11 by ~STUDIOBLINKTWICE on deviantART