Plugin based on GeSHi library, which supports most languages. CodeColorer has various nice features:
- line numbers
- automatic links to the documentation inserting
- code block size calculating (short code would have short block, for long one block height would be fixed and scrollbar would appear)
- code block style customization on Site Admin
- syntax colors customization in CSS file
- syntax highlighting of the code in comments
- code protect from mangling by Wordpress (for example, quotes, double-dashes, etc would look just right as you entered)