According to Game Informer, Gearbox revealed during a PAX East panel that Borderlands 2 will see the addition of a Mechromancer class, along with character customization.  Apparently, players will be able to unlock new wardrobes, instead of just starting out with a specific assortment of gear.

Aside from gear and costumes, players will get access to custom heads, that will become available as unlocks by ranking up, completing missions and challenges throughout the game.  GI says that players of the original game will be awarded with an exclusive head and skin upon playing Borderlands 2.

Keep in mind that the Mechromancer has not actually been developed yet and Gearbox will be releasing it post-launch as DLC.

[Game Informer]