I don't have 10, but a few:

- Thor's battle with Beta Ray Bill to see who is worthy, during Walt Simonson's historic run.

- The FF issue where Gladiator  comes to earth and a battle royale ensues.  Great battle, great cover, all thanks to JB.

I suppose that's really a couple and not a few, but those two sprang to mind immediately.

Thor versus Beta Ray Bill's gotta be up there, and as long as we're talking Simonson's THOR run, I gotta mention the last stand of the Execution in Hel. Truly epic!

Also...

Daredevil versus Elektra (the bear trap fight - you know the one).

Always had a fondness for the brutal throwdown between Wonder Man and the Vision in that issue that set up the Avengers versus Graviton.

Spider-Man versus Juggernaut.

Colossus's bar room brawl with the Juggernaut.

X-Men versus the Shi'Ar Imperial Guard during the Phoenix Saga.

FF versus Gladiator.

Just a few from my childhood there - I'm sure I've got some others that'll come to mind as I think on it...

ok..this is *My* list..Odds are I will change my mind tomorrow..

but these are my first impulse personal top ten fights..

X-Men # 137: "Phoenix Must Die"..I was holding my breath as I read the battle between Colossus and The Gladiator..just praying Colossus would win!  

Avengers #166: An amped up Count Neferia takes on all the Avengers..with great art by "you know who" ;) 

What If # 3: "What If The Avengers Had Never Been?" Gil Kane was at the peak here..Man!!! This comic just weighed down with action packed goodness.. 

Fantastic Four: 250: Gladiator dukes it out with The Fantastic Four..Boy-o-boy did poor Ben Grimm get a whuppin'

All-Star Squadron 36: Earth 2 Superman vs. Captain Marvel!!...Classic...

Superman Annual  #11:  "For the Man Who Has Everything" an epic battle..A real holy smokes moment for me..

DC Comics Presents  #29: Superman vs. The Spectre??, You mean there is somebody out there that can beat..*gulp*..Superman?

DC Comics Presents # 81: Superman vs. The Ambush Bug...This was "coke spurtin' out of the nose funny"

The Flash vol2 #101: The finale to "Terminal Velocity"...wow-e-wow-wow!

Golden Age #4 : When the jig is up and a overpowered "little corporal" dukes it out with the JSA + friends?..A slobber knocker

On top of my head...

X-Men vs Proteus

The Flash vs Zoom (Geoff Johns)

X-Men vs Imperial Guard (X-Men #137)

Any Daredevil vs Bullseye fight by Frank Miller.

Batman vs Superman in Dark Knight Returns.

Now that I am thinking about it, there are so many coming up it is difficult to make a list...

Namor vs. Hulk in Tales to Astonish 100

"Colossus's bar room brawl with the Juggernaut. In what comic issue does that one take place?" It takes place in the 180's(either 183 or 184), Logan and Nightcrawler take Peter to a bar after Peter tells Kitty about what happened off-world in the Secret War.  Nice Romita Jr. art, too.

Robert K.  Live from Austin

I wanna throw in a vote for Walt Simonson's all-splash-page issue of Thor where he fought the Midgard Serpent.

Spider-Man letting the Master Planner's men beat on him so he could catch his breath before he started fighting back was pretty great, too.

A fun JB example that comes to mind would be the two versions of the Thing's fight with Goody Two Shoes.

And, of course, any of the many epic 1970s battles settled via Hostess products.