I just bought a membership with Agency Access and I am finding it to be a very powerful tool. They provide what seems to be an endless amount of names in the advertising industries. They also have great customer service; a rep walked me through a website tour and he has given me a couple follow up calls in the past month, which I was surprised at. I am not sure of the results yet since I just launched my first promo. Now of course you only get out of it what you put into it. For example, they have a pretty advanced search engine to look through contacts. The list is then provided with no names selected with links to the Companies website. You can then either choose to pick all of them your go through the websites to make a more refined listed, which is what I did and why it too me a month to prepare my first promo; this is where your part comes in at.
They also make it very easy to export list in both excel format and mailing sticker template format. Their e-mail department writes the code for the mailers for you, and they have their own print department which you set up mailing with.