If you can take them off the tank and remove them to a safe distance, glass cleaner and a razor blade are your best bet.
Outside glass I have used glass cleaner on. There is a huge huge huge debate over the use of glass cleaner, with the con people saying it diffuses through the glass into the water and can screw up your water. I personally feel that this opinion is of the uneducated kind. Glass is a solid, and ammonia in glass cleaner evaporates so quickly that nothing is passing though the glass into the tank. Of course, if you use glass cleaner, spray it directly on your tank, and have the hood open, any chemical that enters the tank into the water will screw your water chemistry.
I spray glass cleaner directly onto a non-lint cloth (non-printed newspaper works great) and wipe down the outsides that way. No streaks and you can get off all the greasy oily fingerprints better. Razor blades can be used to scrape off any hardness marks, or cruddy stuff that elbow grease doesn't work on.
Inside the tank I simply use an algae scrubby and elbow grease.
~~Colesea