I think it's human nature to bash a store with bad quality or service, so I think it's only fair to share a good experience as well.
I have ordered aluminum from www.onlinemetalsupply before, and found their prices to be better than anyone else's when I just want a small 2' or 4' section of something. Saturday morning I ordered some aluminum bar for a project, but Saturday afternoon, I discovered that I already had a piece that would work. I called their 1-800 number first thing Monday to see if I could cancel the order, but wasn't optimistic.
To my surprise, a real person (a very POLITE lady named "Diane") answered the phone on the second ring. Not only did she say that I could cancel my order, but when I asked if there was any sort of penalty or"restocking fee", she sounded like that was the silliest thing she had ever heard. She added that I should have the money back in my Paypal account before lunch, and true to her word, I got my refund in less than an hour.
I haven't really compared the prices on stainless steel or the other materials they carry (even some titanium and plastic), but their aluminum is around half the price from McMaster.
Edit - Dan - I put this in "General Spearfishing" because the materials they carry are relevant to building guns or other stuff, but feel free to move it to "off topic" if you prefer.