I used a VERY limited palette of acrylic paint on this one: Alizarin Crimson, Yellow Ochre/Turner Yellow, Medium Ultramarine, Black, and White. I don't remember where I read about this particular limited palette (probably on the the Gurney Journey Blog, or something written by James Gurney), but I really like the color variation you can get from just those three colors (and two values). I will have to play with this more in the future. Also, it's much easier to carry and layout the limited palette for the travelling art setup. :-)
This was done with acrylic paint on 6" x 9" Stonehenge (140#) glued to a piece of Medium Density Fiberboard.