I've used a number of products in the past & have stumbled across an awesome one a few months ago. I picked it up at Petsmart & it's called Natures Miracle litter treatment. It was rather pricey (I believe it was close to $10 for a 32oz/2lb container) but it lasts a very LONG time. It says right on the label "Economical-treats as many as 32 pounds of litter". Honestly, I think it can treat a lot more than that! The directions are to sprinkle 2 tablespoons per pound of litter.
I kid you not...this stuff is the bomb! Before I started using this, I could smell that ammonia stinch the day after I changed the litter & now I can't smell a thing after several days. One time I had completely forgot to scoop & change the litter because I realized that I couldn't smell it anymore!
Another cool thing about it is that you can use it for other animals than just for cats. It claims that cats, small caged animals, snakes, reptiles, Pot belly pigs & rabbit urine trays can use this product. Oh..it's also has a money back guarantee...so if you don't like it, you can always get your money back!
Hope that helps you!