I'm curious too. We had been doing so well with using the sunshine to bleach out poop stains. In Michigan we can go days without a nice shiny sun, and the stains haven't been coming out as well. I'm curious to hear others' tricks!
I'm in Chicago and we don't always have the most sun. I use sun when I can. If I can't I find that adding some vinegar to a cold pre-rinse cycle goes well. I have a stackable (read, xs, holds five or six pairs of pants max) washer/dryer and use about a 1/4 c vinegar for a large load. I read somewhere that putting it in a downy ball (like softener) works as well. Clothes end up not smelling like vinegar, are sanitized, and stain free for the most part.
Re: Stains!