I poked around StackOverflow and Google, but couldn\'t find anyone who has put together a comparison of authentication gems or plugins for Rails (I\'m looking for something
Ruby toolbox has a list of the most popular ones: http://ruby-toolbox.com/categories/rails_authentication.html
You can see that Devise and Authlogic are definitely the most popular.
Personally I use Devise. It works well with Rails 3, is easily customizable, and makes it very easy to integrate Twitter and Facebook based auth.