Mercedes-Benz's response to the threat of the BMW M5. The first generation E55 had only 350hp, from a 5.5-liter v8, compared to the M5's 400hp from a 5.0-liter v8. For the current model, AMG had to add a supercharger to boost hp to 470+. Some say the car's frame is too weak for the engine, though.
I'd rather have a 2004 E55 AMG than a 2005 BMW ///M5. The 5-series is getting ugly.