Are there any mods for writing notes on paper or books?

Solution 1:

As of Snapshot 12w17a, the Book and Quill has been added to the game, which allows users to write in books without the need to install any mods. The crafting recipe for the item is a Book, Feather, and Ink Sac anywhere in the crafting grid.

Wurstknifte's Bookmod seems to be a good fit. It adds a new kind of bookshelf that allows you to place coloured books inside of, and you can write (type) in the books. It's also compatible with 1.0.

Solution 2:

There looks to be several mods of this sort around, such as Tomes by PinkEmma:

Or, this one here, Wurstknifte's Bookmod: