@ZipLine-- I'm not too particular about my beard shampoo. I'd just recommend getting one with a conditioner in it. Or get conditioner separately to use after shampooing. Conditioner is a must, it makes hairs very soft. It's helpful before trimming too.
I've never tried one but I have friends who use beard soap instead of shampoo. I think a natural soap with moisturizers in it, such as olive oil soap might work well.