Using an RSS reader to organize my findings, I established a set of categories for each site-type (news, vids, pics, link-sites, general interest, tech, geek, gossip, entertainment, design, art, fashion, and food), and further arranged each site within each category by order of influence. The top tiers were reserved for "mainstream sites" â€” sites where most of the sharing was occurring (i.e., the content disseminating sites listed above). The lower tiers were reserved for sites that supplied content to top tier sites, but were themselves low on visits.
Left somewhat unsaid, is why you won't be able to do this yourself. Zimmerman has a golden eye for finding content ready to go viral (according to Know Your Meme you can thank him for Rebecca Black). The other thing is how much time it takes. You have to read a lot of the internet, all of it, to find the content other people want to share.
The Nieman Journalism Lab had a pretty good follow up.
Somewhat related, "Is The Free Internet A New God?"
Where do I find content? Mostly from Stellar, Twitter, Tumblr, and RSS, in that order.