I have bought mountains of stuff from iHerb over the years and have always supported them by spreading the word among friends - an excellent customer by any standard. They are cheap, fast and reliable.
But be warned that if they send you a faulty product they will keep your money and not only refuse to put things right, but will actually refuse to communicate with you! I have had jaw-droppingly bad service from them that leaves me absolutely shocked. If you can't go and knock on their door to demand they resolve the problem they will literally just ignore all communication from you and keep your money. They could not care less about customers or their legal responsibilities as a retailer, and I am incredible shocked to have discovered that. I have been stolen from by a company I have supported for years.
Unfortunately they have no PayPal option, so as a consumer you have no protection or other way to get your money back if they choose to ignore your pleadings. So you have been warned!
Fortunately Vitacost have improved their service markedly of late, so I will go back to them. What a shame though.