1. Code Markup
CodeColorer is a code snippet plugin that inserts code that is formatted with the appropriate syntax and highlighting depending on the language.
Developer Formatter uses a highlight system and includes support for over 110 languages, which makes it a one-size-fits-all plugin and reduces the amount of plugins you might need for your site if you include tutorials for many different languages.
5. File Inliner
File Inliner will display the whole content of a file in a WordPress post — perfect to use if your code snippets are particularly long, or if you want to include many elements (<head>, <body>, <scripts>, etc).