I need a way for visitors to rank or rate other visitor’s reviews

One of my blogs has reviews. I want visitors to be able to add their own comments/reviews on a particular product. I also want a way for visitors reading reviews to register agreement or disagreement or give a quality rating to the other comments.

The effect would be under a post where Green Gizmos are reviewed, if somene added a comment or review that no one else agreed with, it would show to future visitors looking over the comments.

If there is something that would allow me to implement this on my site, please let me know. I found plugins that allowed visitors to rate a product (and I do want that too) but I haven’t seen anything where visitors can score other reviews somehow.

Something like Amazon.com’s “23 people found this review helpful” would be great.