I use a castille that a close frined makes for me, but another good castille is kirks. you should be able to find it at the market, but not in the washing aisle, probably in the aisle with the hand soaps and such, but not the cleaner aisle....at least that is how it is in most markets I have seen it in.
I used Fels Naptha one time and it about ate the skin off my hands when I was grating it! Plus the smell is so strong. Kirk's is not bad. I used it to make a batch of all purpose cleaner because I didn't have any of my own castille soap done. The only thing I don't like about Kirk's is that it seems very "sudsy".
1/3 cup grated soap (castile or other homemade soaps work great) 1/3 cup Washing Soda 1/3 Borax
Dissolve soap in sauce pan (with water) combine with other ingredients and 2 gallons of water. Shake each use to mix and use about 1 cup for a full load. Or you can skip dissolving it and just use a food processor/blender to chop and mix everything ultra fine. Use one tablespoon per load.
I have used my own soap before and it works great. I would suggest using a soap that has a low excess fat ratio and I would not recommend using any soap that was superfatted. You don't want the oil from the superfat to coat the fibers of your fabric.
I just wanted to thank everyone for the suggestions for a different soap. I found a 3 pack of the Kirk's castille soap at my grocery store, in the soap section, just as described! Now, to find time to mix up a batch of laundry detergent.