These cars have been sold as the W126, W140, W215, and C216. The original models were not much more than longer versions of the SEC class. They may have been coupes, but they were long enough to be classified as 2 door sedans, or grand tourers.
The second generation W140 was much sleeker than the original car. These were sold from 2000 until 2006. Some models include the CL500 and CL55 AMG, both powered by V8 engines, and the CL600 and CL65 AMG, which got robust V12 engines. There was also a CL63 AMG with a V12 and only sold in 2001. It is very rare and likely to be a collectors item someday.
The third generation has been sold since 2007. Like the earlier version, it has a V8 or V12 engine, with the latter making 510 horsepower. Make no mistake, these cars can move. They'll beat just about any generic sports car on the market, and even give some of the exotic cars a run for their money. They are speed limited to 155 miles per hour, but I "hear" there are ways around that ;)
These cars can be bought at your local Mercedes dealer or on eBay, where you can find good deals on a V8 or V12 sports/luxury car that will cost thousands less than a new luxury car with far less performance.