With the release of the new game today (here and in America), both Xbox and PS3 have released a DLC pack, called "Multiplayer Havoc pack". (it is suggested that the PC has this as well, but I'm not sure how to access it, or acquire it)

It unlocks four Gen1 characters for Multiplayer use & customisation (Wheeljack, Ultra Magnus, Perceptor, Blast Off), for US$10 on PS3 or 800 points on Xbox.

Also, for Xbox users, there is an additional Avatar pack, which can allow you to "dress up" your characters with clothing(?) which is described as "costumes" and "t-shirts". Plus, it includes the ability to add a "pet" Laserbeak or (baby) Grimlock.
Not sure if this will be released for PS3 as well yet.

The link above shows the alt-modes of each of those four - two of which we haven't seen yet - as well as showing off the pet Grimlock.