WP-Syntax provides clean syntax highlighting for embedding source code within pages or posts.
This was a good plugin, but now there seems to be an issue with maintenance and ownership. A couple of years ago I have basically forked this plugin here and actively maintain my version called "WP-GeSHi-Highlight" since then (for instance, I am regularly merging upstream updates from the GeSHi library).
My plugin should be compatible to this one here syntax-wise, i.e. it should serve as a drop-in replacement with no need for you to change your articles.
So, you might want to go ahead and use WP-GeSHi-Highlight instead: https://wordpress.org/plugins/wp-geshi-highlight
I tryed it and it has a nice set of functionalities, BUT is not usable because it makes the page with the embeded code terribly TERRIBLY slow, and I tried it with quite a few diferent computers.