Announcement:
As of June 2012, free social media icon sets Somacro and Somicro get an extra icon for the image-based social network Pinterest. The icon for Twitter has also been updated to its new logo and color (because hey, yes, Twitter now has a slimmer bird).
If you are interested in downloading the free icon sets, simply click on the images below to reach the page of each series (you will then find the download button is at the bottom of the page).