Check out a website called iherb.com. They have loads of supplements and are quite reasonable priced. One brand that is supposed to be good is healthy origins, they do a very potent probiotic with 30 billion bacteria in it which are stomach acid resistant (They do have a few questionable ingredients like magnesium stearate in the capsule for example).
I hear that the soil based organisms in products like the garden of life primal defense are potentially bad for you!?!?!?! Apparently they're spores that can't be killed off and have the potential for harm.
"My mom made two dishes: Take it or Leave it." -- Stephen Wright, comedian