B.J. Penn (Pictures)'s impressive display against Sean Sherk (Pictures) to retain his UFC lightweight championship provided the necessary validation to see Penn emerge as the world's best lightweight.

Penn's lightweight ascension caps a period marked by featherweight and lightweight upsets, light heavyweight activity, the re-emergence of apparent journeymen, and vintage performances by veterans. Although these rankings show considerable movement in the divisions, there is more on the way with a heavy two weeks of MMA action ahead.