I can only speak from the perspective of someone who has taught primary school, not high school, but I really appreciated it when the parents gave me a bunch of nice flowers (who doesn't like flowers?) and I loved the self-made gifts from the children. "My" children made me a book where everyone had contributed a page with a hand-drawn picture of themselves and they had written what they remembered from the time with me. ONe girl wrote how what she was most impressed by how I showed them different tricks with a skipping rope in PE! That book is super-cute,it really is a treasured possession of mine, and reading it makes me all gooey inside.
So, my recommendation: Maybe you could make your teacher(s) a card and write inside how you appreciate that they wrote recommendations for you and what you will remember from their lessons? I don't know though if you are crafty and I can't tell if your teachers are the sort of person who would appreciate something handmade. That, and/or some flowers would be my tip.
Anyway, that's the gift I give to my Spanish teacher and piano teacher before the summer and before Christmas, and if they're not really good actors, then they seem to appreciate it.
