As a part of a teaching family.... steer away from mugs, apples, lotions, candles.... They get SO much of this stuff that they can't possible use it all.
VERY much appreciated items are gift cards to restaurants, school supply stores, movies, etc.
Many teachers spend their own money for supplies in the classroom and truly appreciate things for the classroom.
My daughter is now a senior and a few things we've done that were "hits" were..... giftcard for movies and snacks for 2, starbucks, Staples office supply, bookstores, a gift card to a favorite place.... Sonic is popular, other restaurants, etc.
I typically spend about $25 for teachers she really loves and who have helped her. This year, she had 4 teachers send rec letters to colleges for her and we gave them $20 giftcards and a handwritten thank you note for their help.
They love anything handmade by the student.