(In no particualr order. . .)
Roy - At first, I was completely against Roy, him being just a clone of the more popular Marth. However, if they "Luigitize" Roy and make him his own charactor, completely revamped, then that's how I see Roy in here.
Luigi - Could be from the Sub-Con games, or maybe even Luigi's Mansion (Super-Smash?), but he will be revamped again in an attempt to make him "his own" charactor.
Peach - Super Princess Peach. Sub-Con games. I need say no more.
Bowser - He's that bad dude we ALL love to hate. Plus, he's excused by being playable in a few Mario Games, most of note the Legend of the Seven Stars.
Yoshi - Who could NOT love that egg-selent steed? Plus, I think his position in the very first original SSB comercial kind of seals him in.
DK - Was also in the commercial, and has his own series (one of the many that was jump-started with Mario's help). Though nobody really likes playing him, he just has to be in there, ya know?
Fox - Okay in my book so long as he is accurate to the Adventures storyline. All you Fox lovers will love swinging around a slightly magical stick at people
. Though I am unsure about the safety of "the shine."
Ice Climbers - I sense a strong rebirth for the Ice Climbers not only in Brawl, but with another presence coming with the Wii as well. This is just a feeling, though, and only time will tell the truth.
Ness - Was in both Super Smashes, and though he's from a relatively mediocrely advertised RPG who is only leeching his life from Super Smash Brothers. . .uhh. . .what was I going to say?
Jigglypuff - There are so many times when the Song is just enough. There's just something about Jigglypuff: a cuteness that rivals even Pikachu. And denying her after BOTH Super Smashes and a mild fanbase to boot (most of which DON'T spam Rest
, which, I think Rest should only heal at the cost of sleep, like in the real Pokemon games) would be. . .wrong. Just plain wrong.
Marth - Fire Emblem has a growing fanbase, and so does Marth. However, I DO sense a nerfing in his future, unfortunately.
There is one entity that MUST NEVER RETURN: IF NOBODY ELSE gets kicked out, then for goodness sake kick out
Falco - Not only a clone, but not even a playable charactor in the Starfox games! I HONESTLY don't see why even FOX was PUT in the original SSB anyway when he didn't HAVE any of the fancy moves he had in any of his previous games. Heck, he didn't even have most of them in his only game where he actually gets on foot for the action: Starfox Adventures. If you took Fox from the Adventures game and made him more accurate to charactor (he will still have his laser, don't worry, he just could never use his laser on Dinosaur Planet due to the unstable nature of the planet), THEN he would be more excuseable, but I hardly see it as retroactive. And while Fox is questionable, Falco's INEXCUSEABLE.
EDIT: if you didn't notice, I kinda excluded most of the clones, because I feel that a tolerance for clones will be reduced to ZERO with the coming of the ULTIMATE Smash game. I also excluded ALL of the charactors that were never even PLAYABLE before SSBM, and therefore, shouldn't have been there in the first place. The rest of the ones I removed I just felt didn't make sense.