Unobtrusive, self-hosted comments function to put onto existing web pages

If you really want an easy to use solution, then just download the intensedebate or Disqus comment HTML and you can leave spam checking, OpenID support, Comment sharing, and every other cool feature to them. You get the comments with no work!

It's a win-win. Then later on you can use their API's to pull the comments and put them in your database if you want to switch to a home-made solution.

This also means that you can still get SEO from the comments because when you pull them from the API you can display them in an <noscript> tag or hidden div for the search engines.

This?:

http://www.gentlesource.com/comment-script/ - paid if used commercial, but...

http://cellbiol.com/scripts/free_php_guestbook/free_php_guestbook.html - flat-based, weird design of page (... :]), but has free and simple version

http://www.playaparaiso.org/talkback/doc/ - free, they "require" small donation if you want to remove their logo