If I recall correctly, Sakurai said there would be a max of three third-party characters in Brawl since he wanted to keep the focus on Nintendo. We already have two characters that are pretty epic...will there be a third? Personally, I'm skeptical.
If my vote counted I would give it to one of the epic vampire slayers from the Castlevania series, though the popular vote seems to be Mega Man. Inafune said he wasn't in Brawl a few months ago...I doubt they had enough time to put him in, and why they would wait so long to add him would be beyond me. Mega Man is probably out, in my opinion. If it isn't Mega Man, who do you think the most likely candidate is for that third slot, or do you think they just stuck with Snake and Sonic in the end?