I threw it all together using google-code-prettify and jQuery. The prettification code works pretty well, but it assumes you have your HTML in a form where the
<pre> tag has
class='prettyprint' on it. Because my blog post HTML is all generated using Markdown, it was easier to add the class dynamically with a little more JS and then kick off the prettification. Of course, wanting to do things correctly involved picking a JS library so I didn't resort to using the onload attribute...you get the point.
Of course, rather than me telling you all of this, you can just look at the end result, which I think ends up looking pretty good. Enjoy!