Host family gifts are always kinda tough, if you do a search I think there has been a lot of discussion about this on this board. The first time I studied abroad I brought a picture frame, and then at the end of my time with them I gave them a photo of us to put in it. They seemed to really like it. The second time around, I tried to be a little more original, I brought them a book of photos of my home town, Chicago, along with the picture frame. The book turned out to be great because it kinda served as a "break the ice" kinda thing for my first night there, with them asking questions, me telling about my favorite places in the city, etc.
Good Luck!
Kelly
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"Ojos que no ven, corazón que no siente."