Prism is lightweight (1.5KB minified & gzipped), can be integrated so easily (just insert a CSS and JS ) and works fast. It is already used to beautify lots of code in Dabblet (an interactive CSS playground) so its pretty stable. New languages can be added and the functionality can be improved with the plug-in architecture and the /feel can be completely styled via CSS.
GeSHi is a highly customizable syntax highlighter that can be used to better present code snippets in websites. It is developed to be used in phpBB forum software but is also presented for separated use. This syntax highlighter supports almost every popular language like ActionScript, ASP, C, , , Ruby, SQL & (even robots.txt).
Highlight.js is very easy to use because it works automatically: finds blocks of code, detects a language, highlights it. It has support for 3rd party applications and provides a Firefox extension for viewing code that doesn’t have syntax highlighting.
This online highlighter tool offers many coding languages you can choose to highlight together with several options, you can check/uncheck before highlighting code, Combine Style and HTML Code, Highlight inbuilt keywords, data types etc., Strict Mode, and Wrap overflowing text.
Lighter is a syntax highlighting class developed for MooTools. It was created with the MooTools developer in mind and takes advantage of many of the Framework’s features. Using it can be as simple as adding a single script to your webpage, selecting the elements you wish to highlight, and Lighter takes care of the rest.