I decided it might be useful to start this thread as a place to discuss and post images that could be useful for all the skinners and model makers out there.
I'll start by providing some links to sites that I find useful for reference in skinning:
WWII in Color
This site is well known, but if you go to their forums you will find thousands of more user posted pics an interesting topics of discussion for those interested in the historical aspect
a great site with all sorts of camo swatches from different nations throughout history to the modern day, searchable by country.
Armor Ship and Aircraft Blog
This guy always has interesting pictures and illustrations on his blog.
Personally I find that well researched color illustrations can be more useful than B&W or color retouched photos for skinning so here is an illustration that I found interesting: