I'm in the middle of a rebuild and had this same problem with my large glass top. Razor blades, vinegar, steel wool... none of it cleaned the glass up.
If it really bothers you and you're willing to take the tops off and really clean them, then a product called Bar Keepers Friend is the thing to use. I used the powered form and added a small amount of water to the surface and simply buffed it in with a terry towel (similar to washing a sink with Comet); it didn't take long at all and after I washed everything down with water when I was finished scrubbing, the glass looked brand new.
I'm pretty sure you can buy it just about anywhere although I got mine on Amazon (six bucks a can).