The new Ford Taurus is the replacement for the Five Hundred. The 2009 Taurus was identical to the 2008 Ford Five Hundred. Ford found they shot themselves in the foot by dropping the familar Taurus name, so they resurrected the name.
The Fusion is a smaller vehicle. It replaced the mid sized Contour a few years ago. It is a respectable vehicle, especially the Fusion Hybrid that outperforms the Toyota Camry Hybrid (no small feat).