I just found this fantastic website that "attempt(s) to gather and sort fascinating letters, postcards, telegrams, faxes, and memos" of famous people from Conan O'Brian to Adolf Hitler. Seriously, a fantastic collection of primary sources.

Letters of Note

For instance, there is one letter Albert Einstein wrote to the philosopher Erik Gutkind where, after reading the latter's book, he wrote (among other interesting criticisms and points), that;



Here is another one I found really amusing. I honestly don't have any idea as to the author's book or its content, but something tells me I would really get along well with him. The sign-off with the blurb in question is classic.

Awesome.

Give the site a look through and post anything interesting you find. I found some other really good letters from George Washington and so on, so you are sure to find something interesting.