Where do I put custom classes in Rails applications?

Today Simon Harris asked:

Where [d]o Rails peeps place classes that are for view rendering?

In this case, Simon has specific classes which are used for rendering his views, rather than helper methods.

For Rails 3, any folder inside the app directory is automatically added to the load path of the application, so Simon can put his view rendering classes under app/renderers and then these will be automatically loaded by Rails.

In previous versions of Rails, the best place for these would be in the lib directory in a folder called renderers, which should then be required manually in an initializer (config/initializers/renderers.rb).