If you mean cleaning the outside i have found that ordinary glass cleaner sprayed on a piece of newspaper gives a clean streak free surface. Just make sure that you dont spray the cleaner near the tank, I usually do it in another room.
Newspaper is excellent for a streak free finish I agree.
I'm more interested though in how people clean the inside glass. I'm paranoid about scratches as they show up pretty bad on metal halide lit tanks.
GSA is a bit tough to get off with just a cloth which is pretty safe otherwise for just diatoms etc. I don't trust magnet cleaners as I believe they can cause scratches. Razor blades for me are equally scary. I haven't ever tried the credit card method.
Credit cards work great for me. Since they are made of plastic which is softer than the tank glass, and don't get rocks etc. stuck in them, the chances of scratching are pretty slim. That's all I ever use.
I am a big fan of the mag float brand, ive used it for several years since I first saw it in stores in southern illinois, If you buy the size appropriate to your tank it has a very firm grip that i have never had gravel, snails, other things that scratch get under it. Just so long as you connect the magnets near the surface.
I use a mag float. But I don't like it. Actually I love the conveinence, but have scratched my glass with it several times and I am real carful. But it does not matter how carful you are, you are bound to scratch it. I now use a paper towel on water change days and only use the mag float in between water chages.
I wish there was a good product that would remove scratches from glass.