I'm not bothered about a gift, I appreciate them but don't expect them. I do love getting cards and notes, either from the children or, where parents feels I have been particularly supportive, from them.
Anything handmade by the children is always cherished, a card or drawing is brilliant. I have had a few very appreciated hand-made gifts, including a small hand-painted canvas, a clay rabbit (I love rabbits!) and a photo-frame decorated by the child. Something that reflects my personality is otherwise good (I have gotten a lot of rabbit stuff in my time but I do like it all!).
Outside that you can't really go wrong (for me) with chocolates, wine or toiletries. Not necessarily very imaginative/personal but I will use at least use them. I have been given things like scarves or jewellery before which, whilst I appreciate the thought, is so often not to my taste and just ends up going to the charity shop. Pens are also always appreciated! I've never received vouchers but for a small amount or a specific experience (eg: afternoon tea) they'd be appreciated, I would feel uncomfortable receiving anything with a very high value though. I've never known a school where they did collections for the teachers rather than individual gifts and don't know how I'd feel about that.
For me the sad thing about the end of the year is having to say goodbye to my current class who I have grown to love and so having a hand-made card or gift to remember the child by and cherish is lovely, I am quite sentimental! Other gifts are appreciated but in honesty if I want wine/ a new mug/ chocolates etc I can go out and buy them myself. I could never go and get myself a beautiful card hand-drawn by one of my students and the memories that would evoke so that makes it special.