So I've been reading this website, stepfamilyletterproject.wordpress.com, and there are some posts that totally prompted me to sign-in and comment:

You can read one here: http://stepfamilyletterproject.wordpress.com/2009/01/15/dear-wife/

And here are some nice letters to stepmoms:

http://stepfamilyletterproject.wordpress.com/2009/04/09/dear-stepmom-2/

http://stepfamilyletterproject.wordpress.com/2009/02/01/to-the-new-wife-...

http://stepfamilyletterproject.wordpress.com/2009/01/17/dear-all-stepmoms/

http://stepfamilyletterproject.wordpress.com/2009/01/15/dear-stepmom/