Thanks to the support of Google Summer of Code'09, I was able to develop the Recommender Bundle for Drupal, which includes the following modules:

http://drupal.org/project/recommenderhttp://drupal.org/project/history_rechttp://drupal.org/project/fivestar_rechttp://drupal.org/project/voting_rechttp://drupal.org/project/uc_rechttp://drupal.org/project/similargroupshttp://drupal.org/project/media_rec (not developed)

Basically, the modules make content recommendations based on such criteria as "Users who viewed this node also viewed", or "You might be interested in these nodes because you have visited similar nodes". Please refer to the project description of each module for more details.

Followup new features development and code maintenance would be coordinated through the issue queue of each module. Please feel free to use it.

Have fun using the modules! :)