Northern Brewer and
Midwest Supplies are both great retailers. I'm fortunate enough to live close to both, and use both, depending on which is more convenient at the time. Never mail ordered from either, but I've heard great things about both of them in that respect - I believe Midwest may be a little cheaper.
I know they give at 10% discount to AHA members in the stores. Not sure if it applies to online orders or not, but might be worth checking, if you're a member.