Sheila, I am also a teacher, and I agree with everything you posted. I wanted to add that for a teacher's gift, besides the personal letter (my favorite to receive) or a gift card, two other gifts that I like receiving are bath and body works products and plants/flowers.
I bought a 12-pack of 120 minute phone cards from Costco for $49, which can be used to call almost every country from the USA and from some places abroad. I plan to distribute one or two in addition to the my tip to the cabin steward, waiter, etc. I know cash is the preferable gift, but they will be receiving a generous tip from me too...I simply want to tack on something small that's thoughtful and personal.
There has been much controversy and many debates on this board about giving out phone cards to the crew. Here's the way I see it: The crew always calls their home country from the various ports, and while these particular phone cards might not be usable at every port, if at least one port is in the USA, it will be a useful and practical gift.