Released comment system
I just released the code for the comment system I'm using on this blog, another secret blog, and my photo site which is also secret. The comment system is implemented as a web service you run internally. Your interesting web site calls over to commentServe when it wants to show existing comments or render an add-comment form.
It's a poor man's self-hosted Disqus, but it still has spam filtering, notifications, HTML support, RDF integration, and some other things you wouldn't normally have if you just hacked one of these together for a day. (You'd probably exceed my system if you hacked for two days, however.)
Source: http://bigasterisk.com/darcs/?r=commentserve;a=tree
Readme: http://bigasterisk.com/darcs/?r=commentserve;a=headblob;f=/readme
Github mirror: https://github.com/drewp/commentserve