I always have friends of the family asking me what they should buy their favorite teacher. My first suggestion is to buy them something your child thinks of: often, your child will know what their teacher likes more than you realize!
But, for those who want a clear suggestion, I do have a few other ideas. Especially for teachers that embrace the world of technology! If you have a teacher that stays up-to-date with tech, I highly recommend these gifts. They'll be invaluable to the classroom, and help both the teacher and the students!
Gifts cards: You can get personalized gift cards for the Apple App Store, Google Play Store, or even for a site that sells tech goods like Amazon! This way, the teacher can get apps that will help improve the classroom, or buy some goods that the room has been lacking. You could even suggest some apps you believe they might like for them to purchase with the gift card! Also, gift cards for local book stores is always a good choice, especially for English teachers. I won't say that all teachers love to read, but come on, most do!
Mini speakers: Often, classrooms don't have great speakers, but a mini pair can be perfect for small projects, or just for the teacher to enjoy when they are on break in their room!
Backup battery charger: No more need to recharge your phone with a wall charger! This device allows phones and tablets to be recharged on the charger, rather than through a wall socket.
Virtual Keyboard or Bluetooth Stylus: These gifts are only good if you're doing a class gift! If you're all chipping in with other parents, getting a teacher that uses tablets in the classroom a stylus or virtual keyboard can make the technology even more efficient.
Lastly, and this one's personally my favorite, make a donation in their name! Find a charity related to their favorite subjects, and make a donation. Give them a card telling them what you did, and you know that they will love it!