You might want to ask an admin person in the department what the gifts policy is, before you spend on something fancy that the person can't legally accept.
Are you sure a gift is appropriate even if legal? If you're a good student and not too antisocial they should be happy to recommend you, and might feel a little uncomfortable about getting something "in return" even if that's not how you mean it.
Of course if gifts are expected at your school, then never mind -- how about Amazon gift certs?