Add commenting to your website
Echo - An impressive feature set that includes the ability to upload pictures. It allows extensive customization and attempts to integrate all social networking sites into your comments platform. There are free and fee versions. It works very well, and techn support for paid customers is prompt and effective. I use this on my very popular barbecue website AmazingRibs.com
Disqus - Many consider this to be the best, but their support leaves a lot to be desired. Broken links on their website, and slow response times. There are two versions, a free option and a premium pay option. I am not impressed.
IntenseDebate - Super easy to set up and very powerful. Free. But erratic. On one site a page would have two sets of comments, one for http://page.com and another for http://www.page.com, the only difference being the www! Sometimes replies by the admin do not post at all. Support is poor. I used it for months and dumped it.
There are other services I have not tested:
InstaComment - Simple barebones free system.
Polldaddy - Another way to add ratings to your site. Also does polls and surveys.
Rating System - Add ratings of products, articles, comments with this service.