Ok, so this has probably been done before, but…
along the lines of “Bambi Meets Godzilla”, I submit:
The Beatles Meet Darth Vader. The Fab Four sing of peace and love. Vader decapitates them with his lightsaber.
Teenagers vs Jason, Freddy Krueger, or Michael Myers.
Rambo V (Adventures in Mayberry.) Instead of the Sheriff Teasle and the Washington State National Guard, this one will have Rambo take on Sheriff Andy Taylor and Barney Fife.
SSG Schwartz
Superman vs. the Mole Men?
Lennox Lewis vs. either of the Olsen twins. Or both of them, really.
In a battle of the comedians, Andy Dick vs. Patrick Warburton. (I hear Dick is looking for a comeback after the John Lovitz loss.)
I thought Superman was on the Mole Men’s side.
How about Superman vs. that asshole in the diner near the end of Superman II? That guy beat Superman up earlier in the movie when Superman lost his powers. Little did he know who he was dealing with during the rematch.
British Empire vs Zanzibar
Jet Li vs. a dryer lint trap in need of emptying.
“You are fluffy, my friend. You will not live.”
The Death Star versus a quadriplegic kitten nailed to the ground.
This classic match-up from R.K. Milholland
Dexter versus a member of the European monarchies, especially one of the haemophiliac ones.
The Fantastic Four versus The Telly Tubbies.
Ooooh, I’d love to see Tinky Winky get torched and La La given a good clobbering. I think the other 2 would run as fast as their fat little legs would carry them.
Storm vs. Strom
seodoa vs. an entire army of these little cheesecakes.
Somebody set this battle up now, please.
ETA: Hate to say it, but Strom would totally win. He would use his Mecha-Ultra Segregation Attack to make Storm go sit in the back of the bus. 
Anybody vs. Stephen Hawking
Most amusing - A sober Verne Troyer versus 10 drunken children
Unicron vs. Wheelie
Jack Bauer vs. Kenny (from South Park)
Jack’s a ferocious, torturing death-dealing machine, while Kenny seems to die if you wink at him the wrong way.
Bruce Wayne vs. Lil’ Wayne.
Jack Dempsey vs. Patrick Dempsey.
Bruce Lee vs. Peggy Lee.
Chuck Liddell vs. Alice Liddell.
Archie Moore vs. Roger Moore.
Jimmy Carter vs. Jimmy Carter.
Jack Johnson vs. Jack Johnson.
Roberto Duran vs. Duran Duran.