Buying 1000 social bookmarks and a million twitter followers isn't working that great anymore. Google is getting smarter. However, a diverse profile from an array of social networking sites will DRASTICALLY boost your sites authority, and even get some natural traffic.

These sites are second-nature to many of you, but I compiled a list of my top 13 favorite sites to submit to.

The List:
StumbleUpon - Simply Install the toolbar to submit your site. Remember, You can't submit directly from the site.
Digg - Getting phased out a bit, but the links are still very powerful. Make 2-3 accounts and give your self some "Diggs", this will help add value.
Reddit - A bit tricky, consider sharing a few real posts before seeding your own content. They are picky about spam.
Facebook - Facebook shares are an SEO goldmine! Post the share button API on your site and share your links!
Google+ - This is google's own house. They definitely value this data very highly. (IT AUTO-PINGS YOUR DOMAIN!)
Twitter - They have admitted to using this data, however, social reach is important. Re-tweets from powerful followers are the only ones that count.
Youtube - Again, this is Google's own house. They surely use this data.
Pinterest - Make Sure you get good re-pins. Google has figured out how to detect spam re-pins. This is EXTREMELY powerful, if done right.
Delicious - Easy to submit to, provided categorial submission. Helps boost crawl rate.
Tumblr - Tumblr can be very powerful. Make sure you post some unique content first, this will give your link added value.
Instagram - This is up and coming. At the moment, it might not provide much SEO value, but it will, definitely.
Visual.ly - Great for infographics and data graphs. Make a short graphic for your site, its a powerful link.
Chime.in - This is a PR 8 Backlink, not very well known. Great for getting pages indexed.




Others to Consider: Buzzfeed, Fark, Slashdot, FriendFeed. (Submit to these if you have time, not as valuable as the above sites)

Benefits of These Sites:
Boost your crawl rate/index time - Your site's new pages will get indexed faster if they are on these sites
Organic traffic - Believe it or not, you will get some natural traffic, even if your site is not very viral
Natural links - 1000 bookmarks is not natural, but a diverse presence on these social networks is Very natural.


Conclusion:
Submitting to these sites should be second nature to all of you. In less than an hour, you can get high quality links from all of them, boost your crawl rate, and increase natural authority. MANUAL social submission is one of the only sure-fire ways to boost your ranking without risking any penalty.