Fair Fights

[Dim of the Yard]

Gwen Stefani vs. Yoko Ono
(John had a bed put into the recording studio during the recording of the Let It Be record just so Yoko could be close to him, so she might as well have been a part of the Beatles)

The Fellowship of the Ring (The 9 Walkers) vs. The Justice League

[RobtheBarbarian]

Legolas and Red Arrow

DC
vs
Marvel

[Junkyard]

Powergirl and Sentinel

Matrix and Terminator

[Johnny Unusual]

Should I know who Sentinel is?  Because while I read many many comics, I've never heard of him.  Do you mean the giant robot army, or do you mean Sentry?  Please elaborate.

[Junkyard]

Ah, yeah, Sentry. (Instead of being named after a killer robot, he's named after a grocery store?)

[Johnny Unusual]

Anyhoo, Agent Smith Vs. Skynet (I wonder what Skynet looks like in the Matrix.  Maybe he would just be the landscape)

YouTube Vs. Wikipedia

[GregMcduck]

Evolution of Dance Vs. Evolution (disambiguation)

Actors who've worked with Tim Burton
Vs.
Actors who've worked with Wes Anderson

[Sharktopus]

Bill Murray as Bunny Breckinridge in Ed Wood Vs Bill Murray as the spineless professor in The Royal Tenenbaums

Fictional Rock Stars Vs Fictional Pop Stars

[Junkyard]

The fat guy from Limozeen and Avril Levigne.

Transformers Universe vs Godzilla Universe (AKA Toho Monsters Universe.)

[GregMcduck]

Arcee Vs. Mothra (you could probably get them to stop fighting by turning on the Lifetime Network)

Retired football players
Vs.
Muppets

[RVR II]

Yeah.. Now that'd be a Good One!!

[Junkyard]

Rich Jackson vs "That Huge Hairy One."

Underworld Universe vs Care Bear Universe

[Pak-Man]

Wait Underworld has a "Universe"? :^) Well I'll just make an assumption and say:

A Vampire Vs. Funshine Bear.

Adult Swim Vs. Nicktoons

[Junkyard]

Doctor Quentin Q. Quinn vs JImmy Neutron

Charicters by Charles Dickens vs Charicters by Stephen King

[Tripe]

Bill Sikes vs. Jack Torrance

Dune Universe vs Babylon 5 Universe