PermalinkFu
This is a simple plugin extracted from Mephisto for creating permalinks from attributes.
  class Article < ActiveRecord::Base
    has_permalink :title
  end
This will escape the title, making it fit to use in a URL in the after_validation callback.
Use PermalinkFu.escape to escape a string manually if you like.
If you're having issues with Iconv, you can manually tweak PermalinkFu.translation_to PermalinkFu.translation_from.
These are set to nil if Iconv is not loaded.  You can also manually set them to nil if you don't want to use iconv.
[Added 3.13.2008 by Pat Nakajima] You can now add conditions to #has_permalink like so:
  class Article < ActiveRecord::Base
    has_permalink :title, :if => Proc.new { |article| article.needs_permalink? }
  end
Use the :if or :unless options to specify a Proc, method, or string to be called or evaluated. The permalink
will only be generated if the option evaluates to true.