Are there any often mentioned products or services for adding end user comments to pages that aren't served up by a CMS or blog engine? Assuming the host can execute PHP, Python, ASP.NET classic, or other very common programming languages.
The solution must:
Allow end users to leave a comment on a web page, with an easy login process for the user.
Store and emit the comments in such a way that they can be crawled by search engines, and are indexed as part of the parent page. (The only way I know of would be to in-line the comments as plain HTML in the parent page, using PHP / SSI / etc. AFAIK this rules out all Javascript-based solutions such as Facebook's Comments Box?)
Have very robust anti-spam capabilities, preferably with some sort of heuristics and crowd-sourced blacklists (like Akismet).
Have an administration backend with spam management and batch approve capabilities.
This is related to but still different from "Adding comments to static pages?". There is also the more recent "Facebook comment and other commenting system for SEO".
It would be ideal if the solution could easily be integrated in the HTML using just a Javascript, an IFRAME, or something similar. But a light-weight server module written in PHP or another common web development language is also good.