Wow ten pages, nice.
1. Zant - Twilight Princess
Even though we'll get Debbie, I'd still like to see Zant, he'd probably be a heavier character since he's so top heavy but his movies could give him the speed like teleporting, and using an advancing whirlwind slash much like R.O.Bs spinning arm attack. Zant could also probably have a barrier to deflect projectiles much like when he repels Wolf Link in the cutscene following the Lakebed Temple.
2. Ridley - Metroid
I know he's been more of a boss character throughout the series but he'd make such a wonderful playable character, he seems to have a lot of original moves already at his disposal, unlike Ganondorf, Wolf or Lucas who are nothing but clone characters. Perhaps a little nerfing is all Ridley needs. Id've also picked Dark Samus or the SA-X but if we continue to use Samus as both power and zero suit then adding Dark Samus wouldn't have much of a point.
3. Isaac - Golden Sun
The Golden Sun series is massively overlooked, the GBA and DS games are absolutely wonderful and really are the only traditional turn based combat RPGs i can stomach. Isaac did show up as an assist trophy in brawl but he could do so much more and he has plenty of summons of final smash, he has plenty of psynergy to fill up all of his specials as well as weapon based combat. He'd be such a wonderful character to use and would fit in well with the Zelda and Fire Emblem crowd. Failing Isaac, Felix would do too or even Saturos =]