I use Free Nodelet hack: Syntax colouring. It's nice, and doesn't impose additional load on the PM server. I've put the relevant JavaScript and CSS files on my own server just in case (and for easier tweaking).

The fact that it's JS has one drawback: it can choke on big nodes with large <code> sections (and my experiments with setTimeout were unsuccessful — my JS fu is negligeble). But I find that, in practice, it's not a big deal.