I don't know the issue numbers off hand, but in alphabetical order...

Alpha Flight vs Omega Flight - Alpha Flight (Byrne)
Fantastic Four vs Gladiator - Fantastic Four
Hulk & Sasquatch vs Wendigo - The Incredible Hulk
Hulk vs the Avengers - The Avengers (Underground Hulk cover)
Hulk vs the Avengers & the Fantastic Four - Fantastic Four
Hulk vs Submariner - Tales to Astonish
Hulk vs the Thing - Fantastic Four #25
Thing vs the Silver Surfer - The Thing (?)
Thor vs Beta Ray Bill - The Mighty Thor
X-Men vs Alpha Flight - X-Men (Byrne & Claremont)

And here are two others I had to add...

Sub-Mariner & Atlantis vs the Surface World - Fantastic Four
X-Men vs the Imperial Guard - X-Men (Byrne & Claremont)

Hmmm...  All Marvel books...

A few of my favorites:

Doc Samson Vs The Hulk from Incredible Hulk 314.

Wolverine Vs Vindicator from X-Men 109.

Bullseye Vs Elektra from Daredevil 181.

Superman Vs Muhummed Ali by Neal Adams.

Captain America Vs Baron Blood from Captain America 254.

Thor, Odin, & Loki Vs Surtur from Thor 352 & 353.

Hercules Vs Thor from Thor 356(for laughs, but a great story and fight).

Robert K.   Polish from Austin

Order? Not sure.

1) Machine Man versus the Hulk, 3 issues, 235-237

2) Daredevil/Bullseye DAREDEVIL 181

3) Namor/Iron Man mentioned above.

4) Thing vs Thing, MTO 50

5) Superman/Gogul, "For the Man who has Everything"

6) The multi-tiered fight scenes from JLA 195-197, versus the Secret Society of Super-villains (became a Perez freak after this and a huge E2 Superman/Flash fan as well, making me realize DC comics could be pretty damn great as well).

7) Cosmic powered Dr. Doom versus the FF, final battle, ish 60. The desperation, the sacrifices, one of Ben Grimm's finer moments, Richards the leader who never quits, Johnny Storm throwing himself into it with no hope, and Sue at her most sensually dramatic. Worth gold by truckloads.

8) Hulk versus Namor, and I can't figure out the ish, but it's the Herb Trimpe underwater fight where Lady Dorma is nearly crushed to death by rubble, forshadowing Jarella's death years later.

9) Kingpin versus the arm-in-sling Spider-man, AMAZING 197, this is MY Spider-Man, if I have to choose one version that sums it up.

10) Every golden age superhero versus the Uber-"superhero", GOLDEN AGE ish 4. Death, mayhem, shocking revelations, one of the most realistically cinematic fight scenes every put to paper.

I think that's my top ten. For the moment until more occurs.

 see now I get thinking and there was also the great battle where Batroc and Captain America team up to fight Mr. Hyde

or when the Avengers fought Korvac..

or..

Also...

Acroyear versus Shaitan.

Batman versus the Mutant gang leader in DARK KNIGHT.

New Mutants vs. Demon Bear.

And my oddball pick of the thread: Hawkeye versus Mockingbird from HAWKEYE #4. As a kid, my heart was really in my throat during this one. Very brutal, very high stakes.

QUOTE: Writers take no credit in this topic.

What?

Sure they do.

Unless their description of the fight is nothing more than "a fight ensues", they absolutely get credit. Take the Juggernaut/Colossus throwdown for example. Did NOT spring fully grown from the brow of John Romita Jr - Claremont crafted a whole story around it. Nor did Michael Golden generate the emotional content of the Acroyear vs. Shaitan battle from Micronauts - that would be Bill Mantlo's doing.

Writers get credit too.

How dare you yung'uns neglect to mention SUPERMAN VS WONDER WOMAN masterfully illustrated in treasury-sized glory by Jose Luis Garcia-Lopez!!!  Before anyone calls me "old", i'm semi-freshly 35.