After thinking a bit, I decided to add some art history books. Sometimes one has to study the masters in order to create your own unique artistic vision. I did not study how to paint.
Rather, I took a bunch of art history classes. I would have liked to take a painting class, but the location of the class was like pretty far. Anyhow, I ended up learning about art from history and from how to books.
Since I have already added how to books, I decided to add art history books. There were plenty at the University I went to. The first books I am bothering to add will focus on the works of my favorite painters.
I reference them a lot, when making my own manga pages. Sometimes it is just easy to work with a good reference. Anyhow, this is going to be a pretty big collection. I hope you find all this information useful for your artsy projects.