I'm slowly working on the den... My most recent addition includes these two weathered gray picture frames from Restoration Hardware Baby & Child.
I like that the gray color ties this room into the living room beyond.
I then framed botanical prints from this site. I saved the PDF images, resized them, and printed them from my home computer. I think they look pretty darn good! I love that the prints and frames tie together all of the colors throughout our home.