I just released on RubyForge (http://acts-as-rated.rubyforge.org) a new rails plugin for rating ActiveRecord objects. Though there are two other plugins with similar functionality, they didn't provide everything I wanted, so I rolled my own.
The main difference from the other plugins is the ability to store the statistics of the rating for each object (total/count/average) in the model itself or in an external statistics table. This eliminates the need to issue count/sum/avg calls on the ratings table itself, making it a lot faster to display, and especially to search for objects by rating.
The plugin has lots of configuration options, include all needed methods to include in migrations, and has a very extensive test suite. The migration has methods for creating the ratings table, the rating statistics table and to add extra fields to the model that we want to add ratings to. Whichever way is chosen, the plugin will adjust itself accordingly.
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