Successfully complete the game to unlock the following Autobots and Decepticons:

Autobots

Bumblebee
Hoist
Hound
Ironhide
Jazz
Optimus Prime
Ratchet
Sideswipe
Trailbreaker
Wheeljack

Decepticons

Barricade
Blackout
Bonecrusher
Brawl
Megatron
Mixmaster
Shockwave
Starscream
Swindle
Thundercracker

Decepticon Drones

Dreadwing
Dropkick
Longarm