One thing that we did recently was to make each of the teachers at my son's school a Kudoboard (www.kudoboard.com), which is basically a more fun version of the office greeting card that gets passed around.

Basically I set up a board for each teacher and added a nice message + photograph and then invited other parents + students to contribute. Everyone else added their own kudos, photos, and videos, and then we delivered the online boards as a surprise to each teacher.