Just got back from Asda where I picked up a couple of bottles of AutoChem Glass Cleaner for just 25p per bottle. Not sure if this nationwide but there were loads in stock (at Wigan). It is made for cars but there's nothing to stop you using it on everyday glass.
Auto Chem Glass Cleaner removes dirt, grease, tobacco deposits and fingermarks to leave a streak-free crystal-clear finish. It also contains anti-mist ingredients that help to reduce misting inside the car. Suitable for interior and exterior use on windows, windscreens and mirrors.