Here are the National Retail Federation stats for Halloween 2004, along with the estimated number of children in those costumes.
1. Spiderman 2,150,116
2. Princess 1,837,372
3. Witch 1,290,069
4. Vampire 899,139
5. Monster 820,953
6. SpongeBob 742,767
7. Ninja 664,581
8. Athlete (Football, Baseball, etc.) 547,302
9. Ghost 547,302
10. Power Rangers 547,302
I went trick or treating with the neighborhood kids: 3 ninjas, 3 princesses, and 1 thomas the train. If I were a ninja, I'd be upset to be beaten by Spongebob.