BMW M has literally written history books since their inception back in 1972. The M obviously stands for Motorsport, and for the longest time, that's all that the M division did: take BMWs and turn them into world-dominating race cars. They started out with the incredibly successful 3.0 CSL, which most people know as the Batmobile.
2006-2010 BMW M5 (E60): Prices, Specs, And Features
The E60 BMW M5 is one of the best examples of the performance sedan breed, if you're willing to look past its reliability.