Letters of Note is a fantastic blog: "Letters of Note is an attempt to gather and sort fascinating letters, postcards, telegrams, faxes, and memos. Scans/photos where possible. Fakes will be sneered at. Updated 2-3 times every weekday."
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. Come and hear Mark speak at the ALA conference in Chicago on July 1.