Borderlands: The Monster and the Racer
One of the early missions in The Secret Armory of General Knoxx is to fetch the parts for Scooter to build the “Monster”, which is a new vehicle that he was designing. Once you complete the mission, it becomes the first (and only) vehicle type that you can fetch from any of Scooter’s teleporters.
There’s an early mention during a cutscene load screen about another vehicle type, the “Racer”. It is supposed to be the fastest vehicle available but with less weaponry/armor and a shorter-duration booster.