I have seen very good results by simply adding a Facebook “Like” button on my landing pages. Put it somewhere below but close to where you want the visitor to interact, your email submit, click here button, etc.
Of course you’re going to want some “likes” to begin with so it doesn’t hurt to purchase a few hundred to get it rolling, then it can naturally grow from there.
Some tests I have done showed the like button almost doubled the conversion rate which is pretty huge for something so simple.
Time to add a Google +1 into the mix?