Haloscan comments have long been the favorite service of webmasters who want to integrate comments and guestbooks in personal homepages hosted on sites like Geocities, Tripod or Google Page Creator that do not provide native support for visitor comments.
Haloscan provides a small Javascript snippet that goes inside your webpages (no server-side PHP scripts). Site visitors can click this Haloscan link to leave comments on your webpage inside a popup window that can also be customized with your logo and custom CSS.
Haloscan provides an easy dashboard to manage comments left by visitors on your webpages. There's even an option to block IP addresses. The only downside is that comments open in a separate window and visitors cannot be view them inline with the webpage content.
Another interesting player is JS-Kit - a single line of HTML code that will instantly enable comments on any webpage - no registration or signups. Unlike Haloscan, the users comments appear on the webpage itself in a threaded format.
Webmasters can also change the look-n-feel of comment boxes and how the comments are displayed though there aren't any readymade templates. While JS-Kit is clearly the simplest and most effective commenting solution around, you'll miss the comment management dashboard available in Haloscan.
HaloScan | JS-Kit Comments - Add comments to any webpage.