They're named as the Terminal Velocity Pack, the Movie Legends Pack and the NFS Heroes Pack. Each provides new single player and multiplayer goodies tied to trophies/achievements.
No date is available as these DLC packs are yet to be officially acknowledged by EA or Criterion. The full leaked trophies list is available over at PS3Trophies.
Terminal Velocity Pack
Velocity: Terminal 5
Drive all 5 Terminal Velocity Pack cars (Single Player)
Velocity: First Class
Finish first in every race in the Terminal Velocity Pack (Single Player)
Velocity: On Final Approach
Unlock either Jump Nitrous PRO or Drift Tires PRO (Multi)
Velocity: Terminal Addiction
Unlock Ram Chassis, Drift Tires and Jump Nitrous for all 5 Terminal Velocity Pack cars (Multi)
Movie Legends Pack
Movies: It’s a Wrap!
Finish first in every race in the Movie Legends Pack (Single Player)
Escape the cops in the Shelby GT500 (Single Player)
Movies: Fan Fiction
Get 5 Slam Takedowns while driving with the ‘Movie Fan’ License Plate (Multiplayer)
NFS Heroes Pack
NFS Hero: Need to Win
Finish first in every race in the NFS Heroes Pack (Single Player)
NFS Hero: Six Underground
Unlock all 6 ‘Under’ License Plates (Multiplayer)
NFS: Hero Worship
Win an event while driving with the ‘NFS Hero’ License Plate (Multiplayer)
Need for Speed: Most Wanted released on Xbox 360, PS3 and PC. Currently the only DLC available for the Criterion follow-up is the Ultimate Speed Pack which shows off "five of the world's fastest exotics" in new races.