Mage Knight Kevin has a nice photo tutorial on painting US paratroopers from WWII.
Here’s a nice — if not overly deep — painting guide to ancient and medieval armies.
Ministories has a step-by-step photo story on how to paint a regiment of American Civil War confederates.
Quindia Studios has a basic American Civil War painting guide.
Studio McVey has a short tutorial on painting camouflage patterns on a pair of pants.