We have used PopupDomination as it signs people up to a newsletter.... so if you need a conversion tool, I'd suggest integrating it with FeedBlitz.com and signing them up to an Autoresponder email series which helps them gauge if your product suits their needs

For more on Autoresponders and how to write them and integrate them into your marketing
http://creativeagencysecrets.com/your-guide-to-autoresponders/