There were 4 generations of the Firebird, which is not a lot considering the number of decades this car was produced. The first generation was sold from 1967 to 1969, and it featured the shape that has become known as the "coke bottle" when viewed from the side. These cars look very similar to the Chevy Camaros from the same year aside from the Firebird's split front bumper. These cars were only sold as 2 door coupes and 2 door convertibles. The Pontiac I6 engine was standard, but a V8 was an option, all the way up to a 400 cubic inch beast.
The second generation was sold from 1970 to 1981, and they looked nothing like the previous Firebird. These were cars that were very similar to the Pontiac that Burt Reynolds drove in Smokey and the Bandit, even though that was a Trans Am. There were only V8 engine sold with this car, but some were much better than others. The 455 cubic inch was first sold with the Firebird in 1971 and that model was called the 455-HO, or high output. The 1973 and 1974 Firebirds with that engine were called the Firebird SD-455, and they are rare and highly sought-after by the collectors car market. These engines were probably the highest performing engines ever put in a production Pontiac, and they are considered to be the last of the muscle car engines. Later on in the second generation, the Trans Am was added as a trim package that had higher performance than the base models, although the 455 engine was gone by that time.
The third generation Pontiac Firebird was sold from 1982 to 1992. They were sold as the base model, the Firebird S/E, or as the top model, the Firebird Trans Am. The range of engines on these cars is remarkable. They went from a puny I4 all the way up to a 5.7 liter V8. The top performer was actually a 3.8 liter turbocharged V6 from Buick that was only sold in 1989.
The fourth and final generation Firebird was sold from 1993 to 2002. It was sold as either a 3 door hatchback or a 2 door convertible. It was aerodynamic, like the previous generation, but sales continued to suffer. Some of the most popular cars of this generation were the 1993 Firehawk, 1994 25th Anniversary Trans Am, and 1999 30th Anniversay Trans Am. There was also the high performance LS1 Firebird, featuring a V8 engine from the Corvette, and in the WS-6 Ram Air trim these cars were the fastest Firebirds ever, even faster than the old SD-455 Firebirds. It has been said by many Firebird owners that the Firebird Formula and Firebird Trans Am cars had higher output from the factory than Pontiac was reporting. This was an old trick to fool the corporate bosses and the insurance companies, but it's rarely done in modern times.
There are many Firebirds out there on the market if you are planning to buy one, it just depends on which models you are looking for. Certain high performance and anniversary models might be hard to locate, while lower powered Firebirds are common and make a great first car when bought used. Check on eBay for a huge selection of all Firebird models and lots of parts.