There are many ways to harness the power of your opt-in list, and you should be able to think of at least one every month with a little lateral thinking. Here are a few to get you going:
Offer a free product.
In much the same manner that you attracted your subscriber to your mailing list in the first place, you can duplicate this process from within your list too. When you have another product ready for your market, set up a strategy exactly as you did for your first one. The difference being, is that you write your content, and a link to the opt-in page and freebie, in you next email bulletin - or in a broadcast message.
Ask questions.
Upload a web page into which you've written a survey. Now this survey can be fielded in several ways. For example, you could import a script for a multi-choice drop-down menu-type survey into your web page. Or you can send out a pertinent question that asks each member for a specific example of what's holding them back. With this type of question always ask them to be as specific as possible, because the more focused their answer is, the more you can tailor the answer you give them.
Use Internet partner relationships.
If you have a medium to large sized list, and I mean a list of at least say 1000 subscribers, other experts could be interested in offering your product to their list too - in exchange for you undertaking a similar favor for them. Contact the experts who occupy the same niche as you. You should use this contact with them to your advantage and look to building future business relationships with them.