Everyone should try making their own laundry detergent. DIY Natural is a great site for inspiration. They have an actual cost breakdown which promotes the benefit of making their own. This my version of a DIY Laundry Detergent, which does a very good and safe job on most garments.
I include the (options) because I find that (for me) it does a better job than the basic. The original recipe which inspired me suggested "any bar soap" would do but I have found that Fel Naptha soap does the best work for me. Now, if you have allergies, then go ahead and try the other types of soaps out there, but if you don't, I recommend Fel Naptha.
I wrote the recipe on my actual soap container so that I wouldn't forget. Although I am NOT an OCD type of person, I admit I purposely wrote it on the side of the container that faces the wall so I wouldn't have to stare at the writing and "ruin" my vision of a "rustic" laundry container.
I used a food processor to grate the soap and mix the ingredients, but I am sure a regular cheese grater and a spoon would do (much longer).
The ingredients will never truly combine but it this is a good picture of a satisfying mix. That sock is filled with rice to absorb any moisture that might invade my can and create annoying lumps. No lumps so far, so I believe it works. Yes, I used the "infamous single sock" from the group of leftover socks after the dryer cruise ship is done.
Update: Use only one or two tablespoons per load. It'll last much longer and you really don't need that much soap to clean your clothes. In fact, you can reduce your usage from regular, store-bought laundry soap to the same degree. I use a plain old soup spoon. I don't really measure anymore. Too much stress.
Enjoy cleaner and healthier laundry!