Powdered Laundry Detergent
1 bar plain soap (I use Sunlight, but I have heard of people using Ivory, or Fels Naptha as well)
1 cup Borax
1 cup Arm and Hammer Washing Soda
1/2 cup powdered Oxy clean (I use the generic brand)
Grate the bar of soap and then grind in a food processor until granulated. You should have around 1-1/2 cups of soap. Mix soap with remaining ingredients. Store in a covered container. Use 2-3 tablespoons per regular load.
This makes a plain, unscented detergent. If you want it to be smelly, add 10-15 drops of your favourite essential oil to the mix. The Sunlight makes the detergent smell lemony, but there is no lingering scent on the clothes. The oxy-clean is optional, but I found it makes a real difference in how stains come out of the kid's clothes.
I like to add the detergent first and let the water run over it to dissolve a bit before adding clothes.
Here is a nice site to start with if you are interested in making detergent.