From my experience, ListBuilder Pro provides the most responsive opt-in email leads on the market and at a very fair price, too.
I have higher mail-opening ratios on email newsletters created with ListBuilder Pro Leads than with newsletters other leads--but the ratios still aren't as high as the ones that have opted-in from my website.
With ListBuilder, I generally see purchase-to-sales conversion ratios (for paid products) of around 1:150 to 1:200--and purchase-to-sign-up ratios (for free products) of 1:20 to 1:50. Of course, these numbers will be different for you, depending on what you're marketing and how you market it.
Isaiah Hull
Free - Brand New eBusiness and Internet Marketing Training Course ~
http://www.workathomerightnow.net