The Tabletop Terrain blog has an illustrated article on using commercial wood staining projects to finish a basic paint job on a Warhammer Orc. More generally known as The Dip, this method actually involves dipping the figure in the wood stain, or painting the stain on. The dark stain settles into the crevices of the figures, making it look like you spent a lot of time shading them. It generally doesn’t hold up to close scrutiny, but from a distance, in massed troops, looks good. For more, see the Miniature Wargaming Wiki entry on The Dip.
“The Dip” is a fantastic way to make moderate to poorly painted miniatures look great. Or to turn a basic block painting job into one that looks like you knew what you were doing. This video has a technique for making your own.
The Tabletop Terrain Blog has a nice post on using a dip to speed up the painting of Genestealers for the new Space Hulk game.