Google Code Prettify is great for turning <code> tags into nicely formatted HTML. I personally appreciate how it displays the line numbers, but they don't get included when you copy+paste. There are many themes available but my favorite is the google code. It treats word wrapping well with line numbers, shows each line number, and is styled nicely. The Drupal module allows you to integrate it easily to Drupal.
Drupal Pretiffy module: http://drupal.org/project/prettify
Prettify: http://code.google.com/p/google-code-prettify/
Prettify Themes Gallery: http://google-code-prettify.googlecode.com/svn/trunk/styles/index.html