I have many suggestions but it really depends on their age. You can never go wrong with giving a book as long as it is age appropriate and interesting to the child. Most of the gifts suggested below can be found at www.k12schoolsupplies.net
For preschool age children, you could give action toys like ABC bean bag toss, or sorting toys, model magic or clay, and even puppets.
Elementary-legos make great gifts as well as paints, a microscope, dress up clothes, diary, and puzzles
Middle school-science experiment kits, a game like jeopardy, or a musical instrument
High school- older kids would love a telescope, sketch pad, books, or a camera