Ratings/Reviews plus positioning

Hi all, i’m a newbie here just starting out in the world of blogging. I’m using wordpress not so much to create blog publishes, but as a kind of CMS system to do specific things.

What i’m after is a plugin that allows visitors to write a comment and give a rating for a particular blog/product.

In addition to this i want the rating given to be combined with all other visitor reviews for this and shown in a ‘digg’ style way next to the blog/product title name.

One last thing, i want to then be able to sort all blogs/products within their category into rating order, so the best rated at the top etc.

I’m sure this will have been done at some point, can anyone point me in the right direction of the best plugin, or plugins.

(Note i’m new, so not brilliant on complexed installs!)