Muscle cars are one of those slices of Americana that spread all over the world. The term "muscle car" dates back to the mid-1960s, when the early Pontiacs were fitted with powerful V8 engines featuring tons of horsepower. Mean-looking cars with big engines and more power than most of us can dream of, it's easy to see why so many people fall in love with them.While muscle cars continue to thrive in today's market, some have indeed become classics and in this gallery we celebrate some of the finest ever built. Browse through and get your motor running!1965 Ford Shelby Mustang GT350Those blue Le Mans stripes are recognizable worldwide. The stock GT350 had plenty of muscle, with a V8 and 271 hp. But the GT350R took it to another level. Fitted with Kobra Kustom upgrades, it made things roar with 306 hp.1968 Dodge Charger R/TYou probably recall this one from the 1968 movie 'Bullitt,' racing against the '68 Mustang GT.1968 Ford Mustang Shelby GT500KRKR stands for "King of the Road," and how cool is that? Only around 1,200 of these were built, making them rare and expensive. This beast featured a 428-cid Cobra Jet engine with 335 hp.1970 Plymouth Hemi SuperbirdThis was based off of the Road Runner Hemi, but clearly had a more futuristic look. Aerodynamics was a big thing, as it was adapted for NASCAR racing.1968 Oldsmobile 442The "442" is a reference to the car's four-barrel carburetor, four-speed transmission, and dual exhausts. It went from 0-60 mph in 6.5 seconds and reached a top speed of 109 mph (175 km/h).1969 Chevrolet Camaro ZL1Some purists might say this is the best Camaro ever built, and they might just have a point. The legendary ZL1 had 435 hp on paper, but in reality it had more power (reportedly over 500 hp). Only 69 of these were produced by GM, making it extremely rare and valuable.1970 Ford Torino CobraElected Motor Trend's 1970 Car of the Year, the Torino Cobra was a mean machine. It featured a roaring V8 delivering 375 hp that would take it from 0-60 mph in 7 seconds.1968 Dodge Super BeeEssentially a stripped-down version of the Dodge Coronet, though the Super Bee V8 engine option would put a smile on any driver's face with its 335 hp.1969 Boss 429 MustangThe Boss 429 engine was so big that the chassis had to be adapted. It became famous for winning the 1966 Le Mans.1970 545 LS6 Chevy ChevelleOnly 3,733 LS6 cars were ever made, so these are really sought-after (and expensive) classics. In 1970, Hot Rod Magazine described the Chevelle as "one of the brutes, and all it needs is a way of staying in contact with terra firma."1970 Pontiac Firebird Trans Am Ram Air IVThese are very rare and expensive classic muscle cars. Not so long ago, one was listed for US$250,000.1967 Ford Mercury CougarThe Mercury Cougar stroke the right balance between muscle and luxury. With its distinct grille, and a softer ride when compared to the Mustang, the V8 version still revved up 320 hp.