The chances are good that there are tradeshows related to your niche in your area. If you go to these you can find people who would be interested in joining your list. People are more likely to trust a face-to-face interaction than an online one. These contacts can turn into lifetime customers for you.
In fact, this tip works well whether you have physical products or you focus your energies strictly online.
PRO TIP: Rather than visit tradeshows, why not put one on? Or at the very least be a featured speaker or facilitator.