If you are interested in making your own washes, check out Les Bursley's Resources section's wash recipes: http://www.awesomepaintjob.com/index.cfm/resources.recipes.
If you are more inclined to purchase them, go to Secret Weapon Miniatures. They sell washes made to Les' recipe in 30 different colors: http://www.secretweaponminiatures.com/index.php?main_page=index&cPath=54.
I am not a paid spokesman, but I do use them and love their flow and coverage.