At work, where we process optical glass panels for military LCD displays, we use an industrial cleaner from a local glass shop (or try a clock shop that does the tall grandfather's, or a place like Michael's that does photo framing), and "naked" newsprint. Works well on every car I've tried it on.

And after the first rain/sleet storm after getting my X-Fire, I intend to keep a good coat of "Rain-X" on that back glass.