Captain America: Stern and Byrne (with Kirby a close second)

Thing: Lee and Kirby

Mr. Fantastic: Byrne

Invisible Girl/Woman: Byrne, Kirby

Human Torch: Lee and Kirby

Inhumans: Lee and Kirby

Black Panther: Lee and Kirby

Thor: Simonson (with Lee and Kirby a close second)

Spider-Man: Lee, Romita Jr. (with considerable mention to Ditko and Romita)

Professor X: Lee and Kirby

Cyclops: Claremont and Byrne

Beast: Lee, Kirby (non-furry version), Byrne (furry version)

Iceman: Simonson and Simonson

Angel: Thomas and Adams

Phoenix (Jean Grey): Claremont and Byrne

Banshee: Claremont and Byrne

Polaris: Thomas and Adams

Havok: Thomas and Adams

Nightcrawler: Claremont and Davis

Wolverine: Claremont and Lee

Storm: Claremont and Byrne

Colossus: Claremont and Silvestri

Phoenix (Rachel Summers): Davis

Shadowcat: Claremont and Davis

Rogue: Claremont and Silvestri

Captain Britain: Davis

Psylocke: Claremont and Davis (pre-ninja version)

Hulk: Byrne

Alpha Flight: Byrne

Daredevil: Nocenti and Romita Jr.

Iron Man: Byrne and Romita Jr

Superman: Byrne

Batman: Barr and Davis

Presumably, villains aren't excluded, so...

Doctor Doom: Lee and Kirby (with Byrne a close second)

Magneto: Claremont and Byrne

Doctor Octopus: Lee and Ditko

Green Goblin: Lee and Romita

Loki: Simonson

Kingpin: Nocenti and Romita Jr.

Mandarin: Byrne and Romita Jr.

Wizard: Lee and Kirby

In several cases, I've liked other creative teams better but my "baseline" is (naturally) pretty heavily influenced by who was working on the character(s) back in the formative years, so...

Avengers - Stern, John Buscema and Tom Palmer
Batman - Mike Barr and Jim Aparo
Captain America - JM DeMatteis and Mike Zeck 
Daredevil - Denny O'Neil and Klaus Janson
Defenders - JM DeMatties and Don Perlin
Fantastic Four - JB
Flash - Cary Bates and Carmine Infantino (I prefer Wally and would drop 90% of my DC books if Barry Allen came back, but I still consider Barry to be "my" Flash)
Hulk - Bill Mantlo and Sal Buscema
Justice League - Gerry Conway and George Perez
Justice Society (and related characters) - Roy Thomas and Jerry Ordway
Legion of Super-Heroes - Paul Levitz and "old" Keith Giffen (current Giffen doesn't use the same style)
Superman - Cary Bates and Curt Swan
Teen Titans - Marv Wolfman and George Perez
Thor - Walt Simonson and Sal Buscema
X-Men - Claremont and JRJR

Some exceptions, though:
Aquaman - Steve Skeates and Jim Aparo
Iron Man - David Michelinie and Bob Layton
Wonder Woman - George Perez

And a few skirt both:
Dr. Strange - Roger Stern and Frank Brunner.
Green Lantern - Steve Englehart (for GL #194-200) and Gil Kane
Spider-Man - Stan Lee (thanks Marvel Tales!) and John Romita SR