Here is a cost effective, easy, and (I think) really cool project. I googled "homemade laundry soap" earlier this week. After reading many recipes for huge batches in 5 gallon buckets that gel after mixing I found one at Mod Cottage for a powdered form that sounded way better. After reading the comments on the post I decided not to use the petroleum-based Fels Naptha soap but instead Dr. Bronner's.
Here are the ingredients: Borax. Washing soda. Dr. B's Castile soap. I think you can use any kind of soap that is pure soap. Other sites suggested Ivory or Fels Naptha.
Grate the soap with a small grater or microplane. Then add one cup of Borax and one cup of washing soda. Mix.
That's it. No phosphates. No petroleum. No stink. No yuck. Use a tablespoon of soap per regular load. I have been disolving the soap in hot then switching the cycle to cold before adding the clothing. I have done a few loads and so far so good. Clean clothes.
UPDATE: The soap has been working wonders. I am just about finished with this batch and have my new bar of soap ready to make another. However...I don't suggest using this on cloth diapers. It seems to leave a residue on our Fuzzi Bunz that makes them loose their absorbancy. This didn't happen right away, it took a number of washes. I haven't noticed a difference on our cotton prefolds. I have gone back to using liquid detergent, Arm and Hammer For Sensitive Skin, on the diapers. The diapers are back to normal.