Agrax Earthshade Gloss & Matte
This awesome stuff is a wash that is a dark brown that will bring your miniature to life! It's already mixed for you, just give it a quick shake and use! This one will also add a nice sheen to what ever it is your painting. There is a Matte version as well!
You can see how beautiful it is on the Tiki Chairs and how it colors the bark and adds much more dimension to it.
The Matte one is wonderful for a brown wash withe the same idea but not shiny.