http://www.destructoid.com/hands-on-...wl-48983.phtml
tl;dr version:
New items:
Spring jump pad (the one Sonic uses for his up+B?)
Screw Attack now sticks to you so you can hold another item with the Screw Attack.
Bombs from Starfox. ("a poker chip with the letter B on it"....dude.)
New flamethrower item that sticks to you like Screw Attack
Spiked item (maybe Gordo from the Kirby games?)
Assist trophies:
A Metroid, latches onto characters as they are known to do
Little Mac (NOOOOOO) who runs around and punches the shit out of you
Drill Dozer
A character from Sin And Punishment
(also, the 1up preview mentioned in an earlier post mentions Advance Wars tanks)
Pokemon:
Wailord or Kyogre ("a giant blue whale that can fly")
Latios and Latias (at the same time)
Torchic
Piplup
Venusaur
Snorlax
Final Smashes:
Peach: Zooms in, graphics from Super Princess Peach appear, zooms out, all opponents are asleep and a bunch of life-restoring peaches are on the stage.
Ike: Same as Link's, pretty much.
Metaknight: Grabs onto people and 1-hit-KO's them.
Pikachu: Turns into a ball of energy, flies around like Super Sonic
Zero Suit Samus: Gets her suit back. Yay.