i am building a blog and would like to know good tools and plugins to implement a commenting system.
goto http://www.disqus.com and signup, then try something like norman's disqus plugin
OR:
use http://aboutecho.com/ - it's really nice
One good place to go looking for things you need (for ruby and rails) is the ruby toolbox.
For instance: for commenting you can find all the gems here. I would recommend the act_as_commentable gem.
On the other hand, handling comments is in most cases so easy in rails, it is also very easy to do it yourself, and there are a lot of tutorials out there that explain that in great detail. For example here.
Hope this helps :)
you're probably looking for a CMS system, I've read about Refinery CMS, it already supports Rails 3, http://refinerycms.com/
The absolutely best resource I have found so far (I am learning Ruby on Rails for the first time) is the online book railstutorial, by Michael Hartl. It is a tutorial that goes through, step by step, the creation of a simple but functional social network. Good luck!