ruby script/plugin install git://github.com/smtlaissezfaire/acts_as_tokenizable.git

Add a column named 'token' to your model, as a string:

class AddTokenStringColumnToUsers < ActiveRecord::Migration
  def self.up
    add_column :users, :token, :string
  end

  def self.down
    remove_column :users, :token
  end
end

Then open up your class, and add the following:

class User < ActiveRecord::Base
  acts_as_tokenizable
end

Now when a user gets created, he will have a unique 16 character token:

user = User.create!
user.token # => "3737edeca0f85e76" 

By default, the token will only be updated once - on the first save. If you would like the token to change after every save, you may specify that like so:

class User < ActiveRecord::Base
  acts_as_tokenizable :update_token => false
end

There is currently no advanced documentation for this plugin.