The Wargames and Railroads Blog has a nice article on how to paint a WWI US Marine. Very appropriate in this, the 100th anniversary of the start of the Great War.
WWI
Goodbyeee! WWI Skirmish Rules
Goodbyeee! is a set of free wargames rules for Great War skirmish actions.
Flanders Field WWI Rules
Flanders Field is a set of free wargames rules for the first World War. It lets players conduct regimental to divisional level actions.
Trench Raider: WWI Waraming In Ten Minutes
Trench Raider is a set of free wargames rules for WWI trench warfare.
Jutland: The Rules of the Game
Jutland: The Rules of the Game are a set of free wargames rules for large scale WWI Fleet Actions.