Here is a selection of recipes I've come across.
Suds A La Katie:
(A Fast and Easy Recipe!)
1/2 Cup Borax*
1/2 Cup Washing Soda dissolved in hot water
1/4-1/2 Cup Liquid Castille
(Makes about 2 Gallons of pretty concentrated stuff!)
*A note on Borax- I've heard that it can age your elastic and PUL.
I've also heard that it's absolutely fine. Just sayin'.
Links with other great recipes:
This site sells everything you need to make your own soap AND recipes!
My friend Jessica uses one of their recipes (Powdered Laundry Detergent- My Favorite) with her cloth diapers and loves it!
This one has 10 different recipes!
This one is from the Duggar Family- didn't you know they made their own?
This one has 13 recipes- look for the "CD Recipe" note
on the recipe to see if they are "safe" for cloth diapers.