First of all,
[youtube]http://www.youtube.com/watch?v=v1bQSw7FOUQ[/youtube]
While Super Smash Bros 64 is my favorite game ever, I'm still really excited for this.
Some characters have been announced already, obviously, but that doesn't mean we can't argue over who else should be in the game

-PaRappa the Rapper
-Fat Princess
-The Killzone Dude
-Sweet Tooth
-Kratos
-Sly Cooper
I think Snake needs to be in this game, even though he was already in Brawl. I'd like to see Crash Bandicoot, Spyro the Dragon, and Rayman (as the three games I loved most as a wee lad), as well as Snake and some representatives from the Final Fantasy and Megaman worlds (but I haven't played either series

).
Tomb Raider was a huge series back in the day, so Lara Croft will almost definitely be int he game I think. Me and my friends were talking about this at dinner last night and Jak and Daxter and Ratchet and Clank were both also mentioned.
With the Killzone guy already implemented and shown in the video, I assume the other big names in PS3 games will be rep'd too. Drake from Uncharted, Cole from inFamous, a plain brown LittleBigPlanet sack thingy, something from Resistance...