There is a lot of buzz about liquid laundry soap, but you have to mix up batches of 5 or more gallons at a time. Instead, I have been using a dry mix of:
2 cups grated soap
1 cup washing soda (Arm & Hammer SuperWashing Soda*)
1 cup borax
For the soap I used Fels-Naptha, but also grated any extra soap I had such as the small bars from hotel stays. I put all the ingredients into a zip lock bag which made it easy to mix everything together. I add 1/4 cup of the mixture to a load, but you may need more or less depending upon how hard your water is. You won't get many suds with this mixture, but the laundry seems to be as clean as it would be using regular soap powder.