Free Online Private Diary
There are so many diaries available on the net for free. So many of them are not private and also they are not good looking sites at all.
There are four sites I want to recommend you for writing the private journal or diary.
ldsjournal has a good interface and there privacy also very good. You can make a book of your journal and can get a printed copy of it. But ldsjournal has a limited amount of memory. Besides this they don't force you to upgrade an account. You can download your journal on your computer. Thus you can make a place to write a new entry.
Diary.com has a very good looking and simple interface. You can make your posts private or public with just one click. Also there is a calendar and you can list the things to do.
Penzu is a high security private diary. You can even lock your single post with a specific password. On upgrade they provide military grade security. Penzu has also very good looking interface.
Uinvue is new site. Here you can write a private diary. Also they provide a tool to write a book. Also you can make a family tree and timeline using this site.