• The Matrix: Neo, Trinity, and Morpheus
• Tron: Tron, Yori, Sark, etc.
• The Nightmare Before Christmas: The Halloween Town kids
• The Addams Family: Morticia, Gomez, Wednesday, Pugsley, Uncle Fester, Cousin Itt, etc.
• Excalibur: King Arthur and the Knights of the Round Table
• Rocky Horror: The Transylvanias: Frank -N- Furter, Columbia, Riff Raff, and Magenta
• Fight Club: Tyler Durden and the Space Monkeys
• Star Wars heroes: Han Solo, Luke Skywalker, Princess Leia and Chewie
• Star Wars Jawas and droids for sale
• Star Wars cantina aliens: Hammer Head, Muftak, Greedo, Walrus Man, etc.
• Star Wars bounty hunters: Boba Fett, Boskk, IG-88, Dengar, 4-LOM, and Zuckuss
• Jabba's band from Star Wars: Return of the Jedi: Max Rebo, Sy Snoodles, and Droopy McCool
• Pirates of the Caribbean: Captain Jack Sparrow, Will Turner, and Elizabeth Swann 
• The movie X-Men: Wolverine, Cyclops, Storm, Phoenix, Nightcrawler, etc.
• Resident Evil: Alice vs. zombies
• Battlestar Galactica: Pilots, Cylons, Starbuck, Number 6, etc.
• Farscape: John Crichton, Aeryn Sun, D'Argo, Zhaan, Rygel, Chiana, Pilot, Scorpius, Crais, etc.
• Wizard of Oz: Good Witch and Lollypop Kids
• Seinfeld: Jerry, George, Elaine, and Adolf Kramer
• Nightmare Before Christmas: Lock, Shock, and Barrel
• The Hitchhiker's Guide to the Galaxy: Arthur Dent, Ford Prefect, Marvin the Paranoid Android, Zaphod Beeblebrox, and/or Trillian
• The Marx Bros: Groucho, Chico, and Harpo (Zeppo?  Seriously?)
• Wizard of Oz: Wicked Witch and Flying Monkeys
• Wizard of Oz: Dorothy, Scarecrow, Tin Man, and cowardly Lion
• Back to the Future: Marty McFly, Doc Brown, Lorraine, George McFly, etc.
• Charlie’s Angels
• Flash Gordon: Flash Gordon, Dale Arden, Ming the Mercilous, Dr. Hans Zarkov, Princess Aura, Prince Barin, Prince Vultan, Klytus, and/or Kala
  
• A Clockwork Orange: Alex and the Droogs
• The Goonies: Mikey, Chunk, Data, Mouth, and Sloth
• The Mod Squad
• Reservoir Dogs: Mr. Orange, Mr. Blonde, Mr. Pink, Mr. Blue, and Mr. Brown
• Superman II: Ursa, Non, and General Zod
• Austin Powers and Dr. Evil
• Night of the Living Dead: Zombies
  
• Scrooged (or A Christmas Carol): The Ghosts of Xmas (Past, Present, and Future)
  
• Jaws: Chief Martin Brody (Scheider), Sam Quint (Shaw), and Matt Hooper (Dreyfuss)
  
• Buckaroo Banzai and the Hong Kong Cavaliers
  
• Blade Runner: The Replicants (Roy Batty, Pris, Leon Kowalski, etc.)
  
• Close Encounters of the Third Kind: The aliens
  
• 2001: A Space Odyssey: Dave Bowman, HAL, and a monolith
  
• Frankenstein's monster, Dr. Frankenstein, and Igor
  
• Ronald McDonald, Mayor McCheese, the Hamburglar, Grimace, Birdie the Early Bird, and The Fry Kids
  
• Hellboy: Hellboy, Liz, and Abe
• Fellowship of the Ring: Frodo, Sam, Merry, Pippin, Gandalf the Grey, Maia, Strider, Man, Legolas, Gimli, and Boromir
• Grease: Pink Ladies & The T-Birds
• Gilligan's Island: Gilligan, the Skipper too, a millionaire, and his wife...
• 101 Dalmations: Cruella and Dalmations
• Sesame Street: Kermit, Big Bird, Oscar the Grouch, Elmo, Bert and Ernie, Cookie Monster, Grover, and The Count
• Yo Gabba Gabba
  
• 300: Spartans
• SNL: The Coneheads (We did this one in 2010)
• The Muppets: Janice, Animal and Dr. Teeth and The Electric Mayhem
• The Muppets: Miss Piggy, Fozzie Bear, Gonzo the Great, Rowlf the Dog, Dr. Bunsen Honeydew and Beaker, Scooter, the Swedish Chef, and Sam the Eagle
• Animal House: Toga Party
  
• Transformers: Optimus Prime, Bumble Bee, Megatron, Soundwave, etc.
• Willy Wonka and Oompa Loopmas
• Robin Hood and his Merry Men (i.e., Little John, Friar Tuck, etc.)
• Hellraiser: Pinhead, Female, CHatterer, and Butterball
• The Three Stooges: Larry, Moe, and Curly
• Star Trek crew: Cpt. Kirk, Spock, Bones, Sulu, Scotty, Uhura, Chekov, etc.
• Star Trek: The Next Generation crew: Cpt. Picard, Riker, Worf, Data, etc.
• The Borg: Queen and drones
• The Harkonens from Dune: The Baron, Feyd, Raban, Piter, etc.
• Fremen from Dune: Paul, Chani, Stilgar, etc.
• Harry Potter, Ron, and Hermione
• The Wizard of Oz: The Lollypop Kids
• The Munsters: Herman, Grandpa, Lily, Eddie, and Marilyn
• Red Dwarf: Lister, Rimmer, Cat, and Kryten
• Where the Wild Things Are: Moishe, Tzippy, Bernard, Emil, Aaron, Ira, Bruno, Goat Boy and Max
  
• The Seven Samuri
• The A Team: Hannibal, B. A. Baracus, Faceman, and Murdock
• Universal Movie Monsters: Frankenstein (and Bride), Wolf Man, Dracula, the Mummy, the Invisible Man, Creature From The Black Lagoon, the Phantom of the Opera, The Hunchback of Notre Dame, the Metaluna Mutant (from This Island Earth), a Mole Man (from The Mole People), and/or the Mask of the Red Death (from The Phantom of the Opera)
  
• Ghostbusters: Any four guys in jumpers with backpacks as proton packs

Comic book/Super hero characters

• Arkham Asylum: The Joker, Harley Quinn, Calendar Man, Clayface, Killer Croc, The Mad Hatter, Mr. Freeze, The Penguin, Poison Ivy, The Riddler, The Scarecrow, Two-Face
• The Batfamily: Batman and Robin, Batgirl, Catwoman, etc.
• New York superheroes: Spiderman, Daredevil, Elektra, etc.
• Heralds of Galactus: Silver Surfer, Nova, Terrax, Morg, Firelord, etc.
• Fantastic Four: Mr. Fantastic, Invisible Woman, Human Torch, and the Thing
• The Green Lantern Corps: Hal Jordan, John Stewart, Guy Gardner, Kilowog, etc.
• The original X-Men: Cyclops, Marvel Girl, Angel, Beast, and Iceman (and Prof. X)
• Archie with Betty and Veronica
• Silk Spectre, Rorschach, Ozymandias, The Nite Owl, The Comedian, and Doctor Manhattan from The Watchmen
• Giant-size X-Men: Wolverine, Storm, Nightcrawler, Collosus, etc.
• The Avengers: Capt. America, Ant-Man, Wasp, Vision, Hulk, Thor, Iron Man
• Justice League: Superman, Batman, Wonder Woman, Flash, Green Lantern, etc.

Cartoon characters

• Dr. Seuss's Cat in the Hat: The Cat and Thing One and Thing Two
• Space Ghost Coast to Coast and Cartoon Planet: Space Ghost, Zorak, Moltar, and/or Brak
• Popeye, Bluto, Wimpy, Sweetpea, and Olive Oil (We did this one in 2009)
• GI Joe good guys Snake Eyes, Scarlet, Duke, etc.
• GI Joe bad guys: Cobra Commander, Destro and the Baroness, etc. (We did this one in 2008)
• GI Joe Dreadnocks: Torch, Ripper, Buzzer, Monkeywrench, Thrasher, plus Zartan, Zarana, and Zandar
• The Thundercats: Lion-O, Cheetara, Tigra, and Panthro
• Alvin and The Chipmunks
• Cinderella and assorted other characters
  
• Alice in Wonderland: Alice, the Cheshire Cat, Mad Hatter, White Rabbit, Tweedle Dee & Tweedle Dum, and Red Queen
  
• Goldilocks and the Three Bears
  
• Three Little Pigs (and Wolf)
  
• Boo Berry, Frankenberry, and Count Chocula
  
• Snap, Crackle, and Pop
  
• Goldilocks and the Three Bears
• Voltron's Lions
• Voltron: Keith, Lance, Pidge, Princess Allura, and Hunk
•  The Teletubbies
• Masters of the Universe good guys: He-Man, Tela, Man-at-Arms, etc.
• Masters of the Universe bad guys: Skeletor, Beast Man, Mer Man, etc.
• The Little Mermaid: Ariel, Sebastian, Flounder, and Scuttle
• Flintstones: Fred, Barney, Wilma, Betty, Dino, Pebbles, Bam Bam, etc. 
• PacMan and Ghosts
• Disney Princesses: Snow White, Cinderella, Ariel, Belle the Beauty, etc.
• Teenage Mutant Ninja Turtles: Leonardo, Michaelangelo, Donatello, and Raphael
• Scooby Doo: Shaggy, Scoob, Daphne, Velma, and Fred
• Snow White and the Seven Dwarves
• Aqua Teen Hunger Force: Master Shake, Frylock, Meatwad (and Carl.  Seriously?)
• The Pink Panther and The Inspector
• Muppet Babies: Kermie, Piggy, Scooter, Skeeter, etc.
• Jonny Quest, Hadji, Dr. Quest, Race Bannon, and Bandit
• The Jetsons: George, Jane, Jusy, Elroy, Astro, and Rosie
• The Silverhawks: Quicksilver, Bluegrass, Steelheart & Steelwill, and the Copper Kid
• Care Bears
• The Smurfs: Papa, Brainy, Smurfette, Brawny, Handy, Clumsy, Greedy, Jokey, Hefty, Farmer, Vanity, etc.
• South Park: Kyle, Stan, Kenny, and Cartman
• Speed Racer, Trixie, Racer X, Pops, Spridle, Chimp Chimp, etc.
• Gumby, Pokey, Prickles, Goo, and the Blockheads
• The Simpsons: Bart, Lisa, Marge, Homer, etc.
• Peanuts: Charlie Brown, Linus, Lucy, Sally, Snoopy, Woodstock, etc.
• Winnie the Pooh characters: Pooh, Tigger, Piglet, etc.

Misc./Historical/Literature

Cheerleaders

Hooters Girls

Greek/Roman gods: Zeus, Hera, Venus, Mars, etc.

Jesus and the apostles

Barbarians

Chipendale's dancers

Nerds

Queen Bee and Drones

Sailors

Santa's Elves

Hippies

Mount Rushmore: George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln

Bands

• Abba
• AC/DC
• B-52s
• Beatles: British Invasion on Ed Sulivan
• Beatles: Sgt. Pepper's Lonely Hearts Club Band
• The Bee Gees ('70s get-up)
• The Blue Man Group
• Brian Setzer and the Stray Cats
• Cats from the musical
• Devo
• Duran Duran
• Flock of Seagulls
• Guns 'n' Roses
• Kiss
• Led Zeppelin
• Nirvana
• Poison
• Queen
• Red Hot Chili Peppers
• REM
• The Ramones
• Frank, Dean, and Sammy
• The Supremes
• Robert Palmer and the girls
• The Monkees
• Twisted Sister
• U2
• Van Halen
• The Village People
• ZZ Top

Many group ideas can also be pared down to couples or adapted to include the kid(s).  See these pages for additional costume ideas:

• Solo
• For couples
• For bald guys
• With the baby