I shop there pretty often, as you may already know. I find it makes life easier for me - not only do they make it easy to find some "hard to find" products my family needs (like fragrance free shower products), but I save a significant amount of money on things like vitamins and probiotics. They are definitely less expensive at iHerb than my local stores, and shipping can be VERY affordable, especially if you order "Shipping Savers".
Here are some of the things I like to buy at iHerb:
Palm Oil (this eco-friendly version is not available in Israel at all, and is perfect for making frosting or fudge)
Solgar supplements and vitamins are usually 50% less than in local stores.
Magnesium Tablets (these and many other supplements are quite pricey in Israel and iHerb is a great way to save!)
Stash Teas (I buy these when they are on sale, as the sale price comes out to less than the lowest price I can find herbal teas for locally, and these are just SO MUCH HIGHER quality than teas I can find for an affordable price!)
Vitamin D (so many people are deficient, it turns out! And my doctor prescribed a rather high dose, and what's sold here is very low dose and more expensive)
Probiotics are far less expensive from iHerb than any I've found in Israel, and they don't weigh much!
EO shower gel (we like this kid friendly all-in-one shower product that doesn't irritate our skin!)
Ricola throat drops (these work out to be only slightly less expensive than the local price, so I use them as a "filler" product, never as my "reason for buying")
Witch Hazel (it's really not easy to find witch hazel products in Israel, though there are a few pricey ones. If you love witch hazel, you'll be thrilled with iherb's price. This one is a toner with alcohol in it - some people like the alcohol in it, but if you don't, they also have plenty of no-alcohol witch hazel products)
Coffee Filters (unbleached) - I can find the #4 size locally, but I use the #2 size, and it's so easy to order it, rather than running around town!
Brown Rice Pasta (only when they're on sale, great for people who don't eat wheat! The local equivalent is more expensive unless there's an amazing sale)
Grapefruit Seed Extract (I checked out a similar product, 1/4 of the size, that cost more than twice as much at my health food store! Many people are convinced this extract keeps colds away!)
Essential Oils (I use them in homemade cleaners) - for a fraction of the price of the ones sold here in Israel! Yes, they are real and natural (and not an MLM - HUGE plus!)!