Someone who tries their best to be available to their students when they need him or her.
Someone who is open to answering questions, and makes sure he or she is easily approachable.
Someone who will never berate or shame a student publicly. As in, they praise the student in public when deserved, and if criticism is needed, that is done in private.
Someone who genuinely cares about the individual needs of his or her students.
Someone who will go to great lengths to get a student any help they may need.
Someone who makes learning fun, enjoyable and memorable.
I know these are the makings of pretty much a perfect teacher, and there is no such thing. However, all the great teachers I had and love had the majority of these qualities, and I think this is why I hold them in such high esteem.