New characters shown in trailer, most likely playable:

Kingpin
Rhino
Blob
Colossus
Storm
Jean Grey
Cyclops
Lizard
Juggernaut
Dr. Doom
Iron Man Hulkbuster Armor
Sabretooth

Mentioned in panel liveblog:

Elektra
Silver Samurai
The Punisher
Beast
Gambit
Green Goblin
Iron Patriot (a pre-order exclusive)
Squirrel Girl
Vulture
Howard The Duck