A good DIY project is a dual flush kit. These kits can be installed in about an hour and can save 17,000 gallons per year. ROI depends on family size but typically can be 1 year.

Here is a link to the one I have:
http://Iamenergysmart.com/Toilets-/-Flush-Kits/Dual-Flush-System.html

I agree it is a great way to save money without investing a ton of money. It is also being environmentally responsible and efficient. The ROI is very reasonable as the other poster had mentioned. Overall great way to improve your home's efficiency.

I have a dual/triple/quad flush American Standard in my home that was built in 1998. That means that it is such a poor performer that you have to flushi it two, three, and sometimes four times to get it to fully flush. And American Standard won't do a thing about it! No more AS for me!!

Of course you can do the same thing for under $30.00 here  http://www.beingwater.com/one2flush-dual-flush-kit

http://www.amazon.com/MJSI-HYR270-HydroRight-Drop-Converter/dp/B002NKRR7Y/ref=sr_1_1?ie=UTF8&s=hi&qid=1278240641&sr=8-1

I put in this kit for $20.00

Works great and took less than 10 minutes to install.

Had the opportunity to sell those. After testing them I came to the conclusion that they have a tendency to leak at the rubber boot.  You can check this with a food color test.  Also you need to have a tank that is at least 12" high.

Tested both, no leaking!

It doesn't in a lot of toilets. It depends on the configuration of the old flush valve that you are attaching to. Some are sloped some are flat. Some have the overflow inlet so close to the surface  that there is virtually no surface area for it to seal. Then when you add that the only thing holding it in place is a plastic tie that is connected to the old overflow tube that may be 25 years old, there is a tendency for leaks. I feel that if one is going to rebuild an old piece of porcelain that they have become attached to, that they would want to make a lasting rebuild. I look at drop in kits like the Hydroright compared to replacement units like the One2flush similar to giving a worn out engine a valve job as opposed to replacing it all together with a new more efficient engine. The valve job will last for awhile but in the long run it will succumb to its weakest link.  in this case new rubber in an old worn valve opening.