A cheap way to save water as well as your wallet is to limit how much water you use when you flush. Since we're not in a position to buy a dual flush toilet right now (and it'd be wasteful to get rid of a perfectly good toilet anyway) we limit our water usage by putting a milk jug filled with water in the tank. This limits how full the tank gets, and therefore prevents the bowl from filling too full as well. This also still leaves enough water to...take care of business.
And while I'm on the subject of toilets, I'll take this opportunity to mention we also buy toilet paper made from recycled paper. I thought this would be a tough transition from our cushy Charmin, but it does the job just fine.