Adding a rating system to your blog for posts, pages, comments, videos, galleries can make your blog more interactive.
Most of you use the popular plugin from lesterchan
http://lesterchan.net/portfolio/prog...wp-postratings
The other two less known plugins are still good
GD Star Rating
http://www.gdstarrating.com/
And Finally, a rating system which I adore that I have integrated on a non wordpress site, and they finally came out with a plugin for wordpress called WP Starbox, which uses Starbox by Nick Stakenburg whos a master at ajax
plugin url:
http://wordpress.org/extend/plugins/starbox-voting/
starbox main with details on the different options starbox has
http://www.nickstakenburg.com/projects/starbox/