Ray has a very good point.
My most responsive customers come from sig files in forums like this and JVs with other marketers.
I included giveaways in my post but did not elaborate. Holding your own giveaway is my favorite method. While participating in giveaway events is good, it does produce a lot of freebie seekers and download and go subscribers.
But you set up a giveaway participation once, it's free except for your time, and I find quite a few giveaway subscribers stick around. The key for that is staying on topic to your giveaway item.