I think both Facebook and Twitter will hit the 1-2 spots within 12 months = social networks will be the new search engines!
facebook and orkut are the famous social networking sites.a new application is been added to orkut for promotion...
Orkut is good for if you want to market: USA, Brazil or India... for all other countries is really not worth it I generate traffic and sales using orkut profiles and Communities... but it's really a lot of work!
I'm using Facebook and twitter for my site's promotion.Many say Orkut works well but didn't work out for me.Albeit facebook and twitter networks are growing gradually.
have you tried eZdia which is another social networking and bookmarking site with its unique feature of Knowledge Bucket.
Facebook, myspace, youtube, twitter, blogger, hubpages, and squidoo, plurk, ibibo, ikarma and orkut etc are helpful for your purpose...
Social Media Optimization is the next level in marketing. Social media optimization (SMO) is a set of methods for generating publicity through social media, online communities and community websites. Methods of SMO include adding RSS feeds, social news buttons, blogging, and incorporating third-party community functionalities like images and videos. 700 bookmarking sites are available here : http://sem-webpromotion.blogspot.com/2009/10/social-bookmarking.html
I'd like to say some Social Networks. Such as Wordpress.com,Livejournal.com, site.google.com,blogspot.com,Wikispace.com,Quizilla.com,hom.space.live.com, and so on.
there are many post about it on this forum please search that keyword in this forum you will find many result.
I would highly recommend to you for link backs to your site a Twitter social news and bookmarking site called Twittley.com It gives bloggers and other good content sites a means to post their articles or just cool news you find on the internet. You post your links but it will show your Twitter profile and others will click on it and will see your website in your twitter profile and follow it. If you post an article to your site you will get a link back. I find the site very addicting though and sometimes spend to much time reading articles
GogruMogru.com is one of the best social networking site. It offers the best ever dating india experience, latest hindi songs download; send unlimited free sms in India, & news around the world, highly animated e-cards for every occasion.
here is the ultimate list of social networks.it's huge http://raven-seo-tools.com/blog/1151/the-ultimate-list-of-niche-social-networks