Benjamin Reid is sharing a set of 81 social bookmarking icons named Social Media Bookmark Icon + where it is possible to find almost every social network.
The “+” in the name refers to the continuous additions being made to the set upon user requests.


They come in 3 different sizes:
16*16px
32*32px
122*42px (large buttons)
And, all icons are in PNG format.

Downloads
http://rapidshare.com/files/281094695/SocialMediaBookmarkIcon.zip