Article marketing, if you do it right. I have found that I get the most traffic from ezinearticles.com and associatedcontent.com, and it converts well.
Social bookmarking did not convert AT ALL for me.
What I did with the article marketing - I picked a clickbank topic in an area that I am familiar with, that was on the first page of its category. I created a Squidoo lens - yes, a Squidoo lens, because I have zero web design skills. I made sure that I put my affiliate link on the top, middle, and bottom of the lens and had a call to action on the lens as well. I talked about my experience with this product, why it works well, etc. - typical sales letter stuff.
I wrote a bunch of ezinearticles and linked to the squidoo lens. For most of the articles that I wrote, I made a sale for each article.
If you want more details, please feel free to message me or ask me here on this thread.
Also - I wrote a ton of articles to get traffic to my adsense site. It's now a PR3 and I make anywhere from $2-$23 a day from it. ($23 is a VERY good day.) I don't know that i would ever do that again, though, because the amount of time versus how much I'm making isn't really a good trade off. I feel like affiliate marketing has more potential.