As with newsletters there are a couple of ways of getting subscribers using forums too.

1. Post on forums leaving a link in your ‘signature’ (if allowed) to your opt-in page.

2. Set up your own forum (easier than it sounds) and let the members know that if they join they’re agreeing to join your [...]

Using Forums To Increase Traffic
You can find forums all over the Web with a focus on almost any niche subject you can think up. By far, the Internet Marketing, “Make Money At Home” subject is the most popular forum focus today and probably for more than several thousand tomorrows, too.
It is easy to find forums [...]