I know know much about putting bras on, but I hear that Zafu.com does. They claim that they can point you to a perfect fit. They do this by listening to all your complaints about your current bras, finding out what you like in a bra, then correcting for this in their recommendations. I don’t think they sell direct, but simply point you to appropriate bras from other retailers.
I, clearly, have no first hand experience with this, but if you’re into wearing bras, you may want to check it out.
Oh, and they do this for jeans too.