One of the best discoveries I have made is using vinegar to clean. I had heard for a while that you could do it, but it took me awhile to try it. I mix 1 part vinegar to 4 parts water. When I first started it, I just waited until I finished a spray that I had bought from a store, rinsed out that bottle, and filled it with my new solution. Half a cup of vinegar with 2 cups water fits perfectly into most normal sized spray bottles. I now use it to clean my windows, mirrors, counters, sinks, sink fixtures, and toilets (just the tops; I still use bleach for the bowl). My father even asked one day how I get my fixtures so shiny!
I keep the spray bottles under each of my bathroom sinks so that they are easily accessible. Another way to save is by using white wash cloths instead of paper towels. You can find some good deals on cheap ones, which work just fine. I either store the wash cloths under the sink with the spray bottle or in a nice bowl. I find that I clean more often when everything is within arms reach.
Note: I read from Heloise that you shouldn't use vinegar to clean granite counter tops. She suggested a drop of liquid dish soap mixed with water. On the Today Show, they said not to use vinegar on wood floors, because it will eventually remove the finish.