All tongue-in-cheekiness aside, Dan Ward recommends some very good reading in his Rogue University Self-Study Masters Curriculum for Project Management, and while probably not as notworthy as a proper MBA, PMP, or Six Sigma cert, a Rogue University diploma will look right at home on your office wall.
I especially like that he encourages people to explore fiction and prose in addition to more traditional non-fiction fare. You probably won't find Neal Stephenson, Walt Whitman or Shel Silverstein in the curriculum of any other MBA program, and I believe there is a lot that can be gleaned from seemingly unrelated sources, particularly when coupled with more pedantic material.