For the conveniance of the site-going public, this is a visual guide of the main Transformers of the film, in both vehicle and robot form. The following Transformers seen in the film are:
NOTE: I'm not the best vehicle expert, nor the best Transformers expert. I've researched the topic to the best of my abilities, but any further knowledge will be appreciated. Just don't get edit conflicts with me as I work. ;) - Gunmaster45
The Autobots, or Autonomous Robotic Organisms in full, are sentient robots from the planet Cybertron, sent to Earth to locate the All Spark, before the Decepticons can find it. They are the protaganists of the film.
Optimus Prime
Optimus Prime, voiced by Peter Cullen as in the original Gen 1 series, is the leader of the Autobots. In the film, his disguise form is a custom refinished Peterbilt Model-379 long nosed truck, three of which were built for production. Originally a flat nosed truck had been selected, but the long nose truck gave greater size to Prime, so was ultimately selected. The truck's paint scheme is loosely based on the paint-scheme used on NASCAR driver Jeff Gordon's car. Originally Optimus Prime was mainly red, but red is among the worste colors to photograph, so blue with red flames was used instead. In robot form, Optimus Prime stands 32' tall, and is composed of 10,108 parts.
Bumblebee
Bumblebee is the first of the Autobots to land on planet Earth, as a scout for the team. When he first arrives, he takes the disguise of a rather undesirable and broken down Chevy Camaro 1976 with a fading yellow paint job and black racing stripes. His voice box was damaged in a previous battle, forcing him to use the car radio as his main means of communication in the film. He is found by Sam Witwicky (Shia LaBeouf) at a used auto retailer, and is bought for $3,000. After Mikaela Banes (Megan Fox) questions why he chose to disguise himself as a piece of crap Camaro, he re-scans and takes the new form of a 5th-generation Camaro 2009 model, in reality a mocked up Pontiac GTO with the Camaro Concept's exterior and interior design. Bumblebee in robot form stands between 16-18' tall, and is composed of an unknown number of parts.
Ironhide
Ironhide is the weapons specialist of the team (our kind of guy), and said to be Optimus Prime's oldest friend. He is a battle hardened soldier, and one of the oldest of the Autobots, succeeded only by Prime. According the to CGI animators at ILM, Ironhide's arm cannons had over 10,000 parts each, more than some of the other Transformers in total. In disguise form, Ironhide is a black GMC Topkick C4500-series pickup truck. In robot form, Ironhide stands 26' tall, and is composed of ~ 30,000 parts.
Ratchet
Ratchet is the team medic, and has enhanced senses for use on all species. His disguise on Earth is a fictional build up on a GM Hummer H2 passed off as a "Search and Rescue" vehicle.
Jazz
Jazz is Optimus Prime's 1st Lieutenant as he was in the Gen 1 series. His fighting style and transformation movements are based on the fighting style of capoeira. His diguise form on Earth is a Pontiac Solstice GXP with a silver paint job. He is the smallest Autobot, standing 15' tall. He is composed of an unknown number of parts.
The Decepticons
Megatron
Starscream
Blackout
Bonecrusher
Barricade
Frenzy
Devastator/Brawl
Brawl's tank form is an extremely large prop rather than a real tank, and was originally built for the movie XXX 2: State of the Union; it was modified for Transformers to carry a replica of the "Venus Fly Trap" MCBS [minus the two forks and "dog bone" magnetic mine detonator] and a pair of quad missile launch tubes on the secondary turret. The hull is a modified truck chassis with the rear shortened and the radiator cut off, using a Freightliner diesel engine and rubber band tracks taken from a construction vehicle; it is noticably too light for a real Abrams, as can be seen from how high it rides up as it runs over a car in Mission City. In addition, extras in the Mission City sequence don't seem to have been advised that they should be avoiding a 40-foot area surrounding the tank's turbine exhaust; some are standing in positions where they'd be severely burned if the tank was real.
The main gun is secured using a non-functional travel lock that has a tendency to disappear and reappear between shots, most likely there to stop the top-heavy prop turret falling off the chassis during the car-crushing sequence, as it has no visible hinge to fold down and is not a component of either the Abrams or the Leopard 2, the two tanks the prop is based on. Indeed, the turret visibly wobbles during this sequence. The main gun noticably doesn't recoil; barely at all in one shot of the muzzle, and not at all in another; by comparison, when the CGI version of the tank fires shortly afterwards the gun recoils as would be expected.