As I've noted before I'm using disqus for my comments. Disqus is an external comment system, it can be embedded just about anywhere.
There are some nice points and some negatives right now.
As an external service disqus is completely separate from my blog. I don't need any local auth system, I don't need to store stuff in a local database, and I don't need a server-side language. ;) In other words, it works beautifully on sites built out of compiled static html. And you can even include it into random web pages.