Harsh: Another Rails Syntax Highlighter
Harsh (or Github repository) is "another Rails syntax highlighter" that comes in plugin form and makes it easy to perform syntax highlighting on code in your Rails views. Harsh works in both Erb and Haml views, adopting a rather interesting configuration syntax for the latter.
Harsh relies on Oniguruma (the regex library) and Ultraviolet (the highlighting library) to do its thing, so you might have some extra installation work to do. This is all covered here.
Harsh is MIT licensed and was created by Michael J. Edgar.