Organic or through selling your product. You'll build a quality list, including buyers. Most marketers who want to build a list use adswaps and solo ads, but in my opinion that's dangerous especially in the internet marketing niche. You'll only build a list of freebie hunters who are looking for PLR or MRR products they can give away on their next swap. Unlikely these subscribers will ever buy from you...or maybe just occasionally if you're lucky.

Building a list of thousands as fast as you can doesn't mean you're going to make money sending out recommendations (affiliate promotions). Better to have a small list of buyers than a huge list of opportunity junkies.

Andre