Couples Costume

Jack and Sally (Nightmare Before Christmas)?

Duke and Scarlett (GI Joe)?

Destro and Baroness (also GI Joe)?

Rapunzel and Eugene (Tangled)?

Strider and Arwen (Lord of the Rings)?

Conan and Red Sonja won the best couple award at my last party. And, i have been wanting to see Giorgio Tsoukalos and Alien Chick duo.

I'd do the Barbie and Ken again but trade costumes.

Hermione and Ron

Neo and Trinity

Darryl and Beth

Rocky and bullwinkle

The undead bride and groom is a classic for couples. Sometimes overdone, but I've seen it revamped with new twists.

Otherwise, some more ideas...

• Gomez and Morticia from The Addams Family
  
• The Gatekeeper and the Keymaster from Ghostbusters (ie: possessed Louis Tully and Dana Barrett)
  
• Queen Nefertiti and her husband, Pharaoh Akhenaten

I saw a winning couple who were a Dog and a Fireplug .
She was "Dog" he was Fireplug. she had a can of Cheez-wizz located down there to spray Him with!

I won one in college going a Hugh Heffner and she went as a playboy bunny. Honestly I think we would have won if I had worn a sheet with eyeholes and she had gone as a playboy bunny. But it brings up the important point.... know your audience!

My son and I are going to be The Joker and Harley Quinn. My husband doesn't dress up, so if I want to match someone else I have to go with whatever one of my kids is doing.
A few years ago my son and I went as Mario and Luigi. We bought overalls, long sleeve shirts, and hats. It was fairly cheap (we spent about $5 less per costume than if we had bought pre-made costumes), easy, comfortable, and instantly recognizable.

Carry and a bucket of blood
Container of paint and brush + for those with kids, have the kids be paintings
Cat and mouse
Grave digger and shovel
Any kind of flower and bee
Storm cloud and lightning bolt
And just to mix it up while still honoring The Nightmare Before Christmas go as the zombie clown couple. "That's our job!" "But we're not mean!" "In our town of Halloween!!!"

I'll stop there because I could keep going!

Last year I saw a Richard Gere and Julia Roberts from "Pretty women". They won best couple.
Richard Gere was pretty simple (which the guy loved, since he was not that into it) The Julia outfit was the one she was wearing in the beginning of the movie with the blond hair.
It was really well done.

Some couples costumes I've done in the past..
scarecrow and crow
snake charmer and eaten-by-a-snake
vampire and vampire hunter