We take the kids out of school...I know that's alot of work/headache for the teachers so we always bring them back something...we are in lower elementary grades, so teachers for that age probably love anything Disney.
I have brought back the nice box of Mickey chocolates $14 or so(our teacher had been teaching for 40 years, I knew that she had everything!).... she said they were really good (and she would tell me the truth). I got those at the airport Disney gift shop.
I have brought back the $10 with purchase totebags, lap blankets (they had a beautiful castle one last Christmas). Also, Emporium (and probably everywhere else) had nice magnetic clips that you can hang posters from....they had plastic ones with characters and nice silver ones (more office-type..with the castle). These were a big hit, I guess the teacher's lose those magnetic clips easily....
I think a Christmas ornament is a great idea. Everybody can always use a beach towel too.