I found this DIY cleaner on here and here and it is fantastic because it works!
Here's the recipe:
8 oz. (1 cup) of warm vinegar
8 oz. ( 1 cup) of Dawn
That's it! I put the vinegar in the microwave for about two minutes to get it warm. Then mix the vinegar and the Dawn in a spray bottle. One cup of Dawn seems like a lot to me, but I guess you need that much to cut through the scum. It makes sense. If it can cut through grease and baked on food, it should be able to cut through yucky shower scum!
I sprayed the Dawn and vinegar mixture on the glass and scrubbed with a sponge. I really didn't have to scrub hard or for very long. That stubborn stuff came right off! I had a bucket of clean water to wipe off the soap suds. When I was done, there still seamed to be a little bit of residue on the glass so I just used the glass cleaner I usually use to give the doors a final wipe. Now my shower doors look as good as new!