Here's what we do:
You grate up a bar of soap. I use Fels-Naptha because I like the way it smells plus it's readily available up here. My oldest two kids actually love doing this part (with the smallest holes on a cheese grater) so they do it for me. :)
Then you add 1/2 cup of Borax.
And 1/2 cup of washing soda. I can find Fels-Naptha, Borax and Washing soda all on the laundry aisle in the Walmart and the Krogers that are in the bigger town North of us. The Fels-Naptha cost about $1.15 here and the Borax and washing soda are each about $3-$4, but since you only use 1/2 cup at a time, they last for a LONG time.
Then you mix. Or, you have your oldest mix so you can take a picture. :)
All done. You only need a tablespoon per full wash load. Yes, really. I've never kept track, but I wash at least one load of clothes/sheets/towels/something per day and often two loads and one batch probably lasts me a month or so. I only wash in cold water and it has no problems dissolving the soap. Everyone loves the way the clothes end up smelling, especially when you combine it with hanging the clothes outside to dry. It makes your laundry area smell wonderful, too.
If you don't do this already, it's a super easy way to cut some money out of your cleaning supply portion of expenses. I found a recipe for dishwasher detergent and I'm going to try that next. Will report back. :)