Seth got this started, so anyone else who's done it, show your stuff!
I got my Riv poster double matted and framed about a week ago. I used a dark brown wooden frame, medium charcoal grey matting over a thin dark olive-brown mat. I have it hung on a green wall, and the whole thing looks like it was designed for my living room. It's low key, but came out pretty classy. The photos aren't my best work, but they show what you can do with this print.
http://www.flickr.com/photos/redding_dave/sets/72157630673110878/