I just looked because I thought I still had the list from last year, but I don't. Anyhow, when you buy your tickets Disney will send alittle notice along regarding costumes. It's pretty much common sense though-- nothing to scary or violent, no realistic weapons.
There is also a lot of deabte in regards to adults being too realistic in their disney characters. Some folks claimed last year they had no problems at all, while others said they were told they couldn't wear their costumes. So it remains a mystery as to the final ruling on that.
Last year we went on Halloween. It was really warm. So just keep that in mind. My costume had capri length pants, short sleeved shirt, and sandals and I was still roasting (it was really muggy that night!!!)