I only shop online because being an American living in Japan there's not much available for me here. Since we're military we have an APO box so our shipping isn't crazy.
I have had only good experiances with
www.netrition.com and I know they DO do the affiliate program.
www.amazon.com does too and I know that's not a supplement or nutrition company, but I'm sure a lot of us shop there and it would only be fitting for us to be able to raise money for the site. I just spent $2,000 there in the last month and really, that's not unusual for us. They do sell fitness books as well so that could be the tie to this site. I also shop at
www.drugstore.com for a lot of different things, but they have supplements as well. Their prices are not the lowest but they are average, not high.