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.
[Added 3.11.2009 by Martin Emde] Make permalink_fu update your permalink everytime the dependent field(s) change.
  class Article < ActiveRecord::Base
    has_permalink :title, :update => true
  end
This will update your permalink every time title changes. Rails versions with _changed? methods will reduce the checks 
for uniqueness to only when the permalink field is changed.
Without :update set to true, your permalink will be set one time and subsequent changes to the field
(title in this example) will not affect the permalink field. To regenerate the permalink field,
set it to nil or a blank string within your model.
Old versions of rails without _changed? attribute support will result in the permalink field being regenerated every 
save.
[Bug Fixed 3.11.2009] Permalink was not being checked for uniqueness when set directly with permalink= on rails versions 
with _changed?