Update: The DLC for July 7th has been announced on LittleBigPlanet.com. Here's what it said:
LittleBigPlanet is under attack from the villainous hordes of the Marvel® Universe, and Sackboy must summon all his skill, courage and cunning if he is going to stop their evil scheme and save every Player Moon from certain destruction!
Fortunately our Sack Hero is not alone and will receive help along the way from legendary Super Heroes as he races against time to put a stop to the villains’ dastardly scheme.
Sackboy must battle his way across rooftops and the city streets to reach the villains’ secret laboratory, where he must stop them from launching their deadly weapon, or LittleBigPlanet will be changed forever!
Do you have what it takes to guide Sackboy through four levels of peril? Are you a worthy match for the Super Villains of Marvel? Will you battle side by side with the most famous Super Heroes of all time?
The Marvel Level Kit is out next week, along with the first of four costume packs, and it’s up to you to save LittleBigPlanet before it’s too late.

I for one am getting these.
Level Kit Info:
http://www.littlebigplanet.com/en-us/game_guide/ps3/downloadable_content/marvel_level_kit/
1st Costume Kit Info:
http://www.littlebigplanet.com/en-us/game_guide/ps3/downloadable_content/marvel_costume_kit_1/
-----------------------------------------------------------------------------------------------------------------
LittleBigPlanet is about to be invaded (don't worry, it's the good kind............I think). Starting July 7th and every other week after that, Mm will introduce 4 new Marvel costume packs, each containing 5 costumes of Marvel's greatest Super Heros and (>>>) Super Villains (<<< this is the bad part).
Here's a list of the costumes:

Captain America
Daredevil
Doctor Octopus
Elektra
Ghost Rider
Green Goblin
Hulk
Invisible Woman
Iron Man
The Human Torch
Magneto
Mystique
the Punisher
Roque
Spider-Man
Storm
The Thing
Thor
Venom
Wolverine
Now for the big one: Mm also plans to release a new Marvel Level Kit, which contains 4 levels. While you play these, you will also collect loads of new Marvel-themed music, objects, materials, stickers, and a special “Rooftop” background. More details on level kit will be released soon (perhapes a new feature or power-up for LBP and LBP2?

), so stay tuned.
Source:
http://www.littlebigplanet.com/en-us/news/article/marvel_costume_packs_and_level_kit_coming_july_7th/