Social Share URLs ~ On Github!
A github repo that is regularly updated and retested, with what looks like about ~50 or 60 services listed.
https://github.com/bradvin/social-share-urls
This is much better than the accepted answer. NewsVine, Delicious, Slashdot, Ping.fm, etc., are all non-existent services today. Plus, some important ones are missing, Skype, etc..
