Rubbing alcohol or rubbing alcohol with some coolant will work well. If you're a 'detail freak' you'll need to commit seppuku after using it though, as some of it may drain off of the windshield and get on the finish. You'll also need to pretend that you don't know what's in windshield wiper fluid.
Best is a warm windshield. I have a 4ft baseboard heater with a low/med/hi setting mounted on a lebgth of 1x12, which enables me to place it on a seat and run a cord out the window. Makes a big difference, and is the best technique for deicing that I've found so far. I'm surprised that they don't provide smaller, say 500 watt heaters, under a seat or something with a plug on the front of the car, at least as an option for cold climates.