A combination of things to be honest. In 18 months we've grown our email list to almost 30k (from near scratch) through the following:
* One email warming up an old list of about 1,500
* Promotion across our network of sites (60 ish relevant sites)
* Facebook paid ads (do ok, but you're doing well if you keep it to 20p a click and 50-60% conversion)
* Twitter (useless, like I say)
* Competition sites (probably the major factor - see my post here
http://www.acorndomains.co.uk/internet-marketing/122655-advertising-competition.html#post475705)
* A competition we ran on Sun+ (quite a big impact on our list, but the brands were a bit disappointed with the value they got)
* Prize contributor brand cooperation (their social media, email lists, etc.)
* Competition marketing partners (their social media, email lists, etc. in return for branding on the site)
There's still plenty more ideas we have in the pipeline - and it's worth pointing out that it's the two 'epic' Campetitions we run each year that have the biggest impact on subscriber numbers.
We were lucky to be able to use the leverage our website network gives us to swap prizes for banner ads in the launch Campetition. We raised £5k in prizes and got 3k+ entries if memory serves.
Edit - oh, and thanks
