I'm looking for a general purpose syntax highlighting library, to output to html.
It's for use within a ruby app, so a ruby library would be good, but an excellent utility which can be piped in and out of would do
Also needs to guess the appropriate language to highlightsy by itself
HTML/CSS/JavaScript based syntax highlighter solutions are the most popular and work well with different server technologies including Ruby.
SyntaxHighlighter (RECOMMENDED) is here to help a developer/coder to post code snippets online with ease and have it look pretty. It's 100% Java Script based and it doesn't care what you have on your server.
Syntax highlighting library for various languages at Rubyforge.org. Has built-in support for converting source code to syntax-highlighted HTML.
SyntaxHighlighter for WordPress. It allows you to easily post syntax highlighted code all without losing its formatting or making an manual changes.
Prettify. A Javascript module and CSS file that allows syntax highlighting of source code snippets in an html page.
GeSHi - Generic Syntax Highlighter. GeSHi started as an idea to create a generic syntax highlighter for the phpBB forum system, but has been generalised to this project. GeSHi aims to be a simple but powerful highlighting class, with the following goals: (1) Support for a wide range of popular languages (2) Easy to add a new language for highlighting (3) Highly customisable output formats
JUSH is a syntax highlighting component written in JavaScript. It highlights HTML, CSS, JS, PHP and SQL code embedded into each other. Beside syntax highlighting, it provides links to the documentation for all supported languages.
SyntaxHighlighter for Windows Live Writer at CodePlex.com (just in case :)
And here a few blog posts on the subject: