While I am adverse to put love letter writing on this blog (in no time it would progress to 50 Shades of Grey stuff) I cannot help but put up something about the writings of George Carlin to his wife, Sally Wade. I have not read or brought the book, but I have seen selections. It is sweet and the act of writing someone you are spending your life with is rather amazing. The reviews on Amazon seem to be pretty mixed.
For your viewing pleasure: http://www.lettersofnote.com/2011/04/romantic-mr-carlin.html