Hi Aran,
Social bookmarking is quite essential for any SEO campaign in my opinion. There are many social bookmarking options you can consider such as Facebook, Tweeter, Stumble Upon, Google +, Reddit, Digg...etc. Not only are they a great source of traffic, as Techcrunch recently saw with Google +. SEO Moz also did a good study on the influence of Tweets with regards to SEO called A Tweet's effect on rankings.
I personally would recommend the following: Facebook Like/Share, Stumble Upon, Twitter and Google +. But you have to make your decision based on the audience your site is targeting.
Cheers,
Walid
