Superhero Disney Princesses - I would say this is the greatest ensemble cosplay I saw. Each costume was so inventive and fun. My favorite is Belle's book hammer. So awesome! (This photo was from their Facebook. I was standing way to the left side and my pictures were all unprepared and lame.)
Predator that killed the Avengers - This is a unique, detailed costume with Iron Man and War Machine heads strapped to his waist and Captain America's shield strapped to his back as trophies of his kills.
Zombie Activist - There were a lot of zombies due to the zombie walk and just the fact that zombies are awesome, but this was the best one I saw.
My Little Pony ensemble - There were a lot of MLP cosplayers and this was the only group with a cohesive style and a Celestia!
Russell from Up
Nyan Cat - I saw this adorable kid all over SDCC. Kudos to her mom who held her rainbow all over the place and probably made the costume.
Tony Stark from Iron Man and the Avengers
Did you see any awesome costumes? What are your favorite cosplays?