The best thing to do with herbs is make sure you are getting it from a company with an established reputation. In the supplement industry, you get what you pay for. Do you want it to work, or do you just want it? If you buy something from Wal-Mart, your local grocery, GNC, or Vitamin world you're buying the bottom of the barrel as far as quality and potency. Companies like Solgar, Country life, Solary, Enzymatic Therapies, etc... cost more, but at least they actually work. Personally, I'll take the BMW over the Yugo any day of the week.
Nature's Way is a great herb company, has been around for years, and does third party testing, they're pretty consistent with their herbs. You definitely want the standarized extract over the whole herb. The whole herb is just parts of the plant crushed up and put in a capsule. Standarization isolates the chemicals that work in an herb and gives you a consistant dosage of those chemicals just like a drug. I'm starting Foremost Milk Thistle 175mg Silymarin standarized extract 3 times per day as soon as it comes in. I'll let you know if my liver enzymes go down on my next blood test. They're pretty screwed up right now. They are a new company with european pharmacudical grade standards, so far all my customers notice a big difference in the potency of the Foremost products.
L-glutithione is extremely important for liver health too. If you use whey protein it has been shown in studies to increase L-glutithione levels in the liver. Lecithin has been shown to help remove fatty deposits in the liver as well as EFA's like cod liver oil (Nordic Naturals is awesome and tastes good), flax, primrose, borage, etc... A blend like Total EFA from Health from the sun is a good option too. Phosphatidyl choline has also been shown in studies to help fatty liver. Garlic is awesome as well. I suggest a liver cleanse after a cycle to most of my clients that juice. Renew Life has a great liver cleanse formula that I'm starting on Monday. I've been on testosterone replacement since 2000 and my liver enzymes just came back fairly high so I'm pretty freaked out and pissed off. Drink tons of water with fresh lemon juice too, it's great to detox the liver.