A friend of mine sells Amsoil products and I usually just get my stuff through him.
I am considering signing up for Amsoils preffered buyer program though, it allows you to buy their pruducts right from their website at dealer cost. The annual fee is $20.00 but I beginning to think I would save that much in no time if I was buying at dealer cost.
Go to this site for more explanation on their products, just one more note is their 10W-30 meets MB 229.3 specs. It is an excellent oil that will last 25k miles. I personally can't get myself to leave it in the that long but I have gotten better and now "only" change it a 5k mile intervals