50/50 mix of Isopropyl alchohol and water and a few drops of Dawn dish soap.

(Isopropyl is 89 cents at wal mart for enough for a 16oz spray bottle filled with this mix. The bigger bottle will make two quarts for $1.19 last time I bought it. 70% works, 90% is better, but costs a little more.)

Cleans at least as well as glass cleaner and leaves no film, for less than $1 per quart. (16oz spray bottle)