The idea of a sleeper is simple: Take a normal looking car, and make it faster without changing the looks too much. Sleepers make for great everyday cars because they're fun to drive and don't stand out too much.
I actually own a sleeper... kind of: a 2008 BMW M5. It looks pretty much like a regular 5-Series, save for a few more exhaust tips, a couple of side grilles, and a badge. But unlike a normal 5-Series, this car puts out 500 horsepower from its 5.0-liter V10, sending all the power to the rear wheels via a six-speed manual transmission.
The previous owner painted the wheels and kidney grilles black, tinted the windows, and made exhaust cutouts to bypass the mufflers. I removed the tint, and replaced the kidney grilles, wheels, and reflectors with OEM units to make it look as factory as possible. The one thing I haven't touched is the exhaust.
We want to know: What's the best sleeper car out there? It doesn't have be new, or even a high-powered version of a normal car. It just has to fit into what makes a sleeper a sleeper. Let us know in the comments below.