If I were to start completely over and had to build my list from scratch I would do a few things.
1. I would create a few squeeze pages and offer a free report and do some forum marketing. If you are consistent in your efforts (which should only take 10-20 minutes per day if you are hitting up a few forums each day) you can probably get 25-50 sign ups per week. It doesn't sound like a lot but after a few months you have 1,000+ subscribers. This is also good for building your "brand"
2. WSOs is a fantastic way to build a list quickly. I am doing a report right now for you guys here at JVNotifyPro that will detail all kinds of good stuff about WSOs so be on the lookout for that. Either doing 100% commission up front, doing free WSOs, or war room reports, you can get a few thousand people on your list relatively quickly...and the quality is normally pretty good. Again, this is also great for brand building.
3. Also as mentioned above, launch download page gifts (through opt in) is a good way to build your brand, build a relationship with the product owner, and build your list.
One thing to keep in mind is that building a list is only half the battle. Marketing to your list is just as important. A good marketer can make more money from a 2,000 subscriber list than a bad marketer to a 100,000 list. Provide value, establish rapport, and legitimately want to help your list succeed. Sounds simple but makes all the difference in the world. I want each and every person on my subscriber list to hit six figures online, I truly do. This translates into me providing a lot of value and in return, I do quite well. It's a win-win-win.