Here is a link to some FB plugins, but they let users share your content on their Facebook. I just use AddThis button that does all the bookmarking sites.
But if you mean icons to link to your FB Fanpage or Twitter page, just use your fave image, and add it to a TEXT widget (in the Appearance > Widgets page) in the footer (or sidebar if your theme won't accept widgets in the footer), then add the link to the images to each of your pages.
I would download the image, then upload it to tinypic.com or your own site. Then make a note of the plain URL.
Here's the code to make images links (remove "blank" if you don't want them to open in a new window):