i usually do special gift for main teacher (usually g cert to local restaurant or Barnes and Noble).
for the other teachers, as well as administrators, cafeteria, media center, custodians, et al i have made a basket of goodies (some homemade cookies, some store bought treats- candy, etc) and an assortment of tea bags/cocoa and drop off to the teacher's lounge with a note of gratitude. it has been a big hit!!
ps- this is a great option for GS cookie sale too- if you want to support your local troops but not eat all of the calories purchase cookies and drop off with a note to the teacher's lounge!!