Secret Weapon Minatures hobby products. So much so that earlier this year I picked up a set of the entire line of washes. The benifit is, when I am not sure which color to use, I can try a bunch!
I picked up some fantasy terrain from JR Miniatures and I had some trouble picking out what colors to use. I decided to do a bit of a test, spraying two models grey and then throwing a few different colors of washes on top to see which I liked. As these are only terrain pieces I really don't want to put a lot of effort in. The washes give some shading without too much work.