I've been working on my top ten list, so this is a perfect opportunity to share!
THIRD_PARTY (Includes returning characters)
10. Godot (He's a horrible fit for Smash.. but he's my favorite character of all-time)
9. Phoenix Wright (I don't really want him, but I just couldn't say no)
8. Bomberman (He'd be kind of unique, but not as much as some people think)
7. Rayman (I quite enjoy his games and he's been good to Ninty)
6. Geno (I have no attachment to him, but he's interesting and he could make people really excited)
5. Simon Belmont (They did well with Snake, so it would be interesting to see what they do here)
4. Professor Layton (I love Layton, and I'm currently working on an illustrated moveset for him. Not exactly a perfect fit, though)
3. Solid Snake (Metal Gear is a series I like and I love Snake in Smash)
2. Pac-Man (Can you say iconic? I can! I also enjoyed his games on the Cube)
1. Sonic the Hedgehog (My favorite non-Nintendo franchise and a dude who fit right into Smash. Seeing him on the Dojo made my month)
Please note that the only third-parties I actually would like to see are 1-4 and of course the confirmed Mega Man. The others are rated on how little they would annoy me.
First Party (Only Non-Brawl Candidates)
10. Bowser Jr. (He'd be interesting and would definitely fit in)
9. Dillon (He's an up and coming star and I love his design.)
8. Shulk (Because he's Shulk. Need I say more?)
7. Little Mac (I love Punch-Out... but I see a slight lack of potential here.)
6. Ghirahim (I loved the dude when I was playing Skyward Sword, and I feel as though he's designed to fight in Smash)
5. Mewtwo (Great character, but he's been in before so I wouldn't miss him this time.)
4. Tingle (I HATE YOU, HATEBASE! STUPID AMERICANS!)
3. Palutena (I want someone else for Kid Icarus, and I think she fits the bill quite nicely)
2. Ridley (I'm aware of the sheer effort it would take to make this character. It's worth it)
1. King K. Rool (Oh my childhood! And a perfect fit for Smash, no less! And not a difficult croc to make, either!)
Of course, Rawk Hawk gets an honorable mention. He has no chance in heck though, so I didn't bother listing him.