Plugin provides syntax highlighting for about 116 programming languages via Geshi.
I am glad to accept offers or code patches for the plugin by email: FractalizeR@yandex.ru
Please start PHP code you want to highlight from PHP tag <?php and it will be highlighted just fine.
If you write code in the editor, make newlines with Ctrl-Enter, not just enter. If you paste it - format it using an editor buttor or at least ensure you formatted all source using Preformatted style