Here are some of my favorites:
Vash the Stampede: I realize that there were a couple at NDK this year, but this one was flawlessly in character every time I saw him. He even got a group started with "Love and Peace!" by the bathrooms. Well done!
Any DBZ cosplay: I am glad that this series continues to get some love. I saw a pink-shirt Vegeta, Saiyaman and Saiyawoman, Gotenks, Videl, and a couple Androids and Buus. Thank you for always making me smile!
I was also delighted to see Kusuri-uri (Mononoke) and Yurine (Karas), as well as Gene, Aisha, and Jim from Outlaw Star, and Chrno and Rosette from Chrno Crusade. All of them did a fantastic job on their cosplays!
I'd also like to mention the girl who wore what looked like a wolf pelt and camped out near Artist's Alley on Friday. When she bent over, her costume was so convincing that many people were doing double-takes! And when people went to pet her, she continued to stay in character. Very nicely done.