Though not a new idea, UrlColumn solves this problem in a nice way:

class Page < ActiveRecord::Base has_url_column :page_url, :from => :title end

When you create or save a 'Page', a nice url will be created from the 'title' column and stored in the 'page_url' column.

"My Lucky Biscuit" becomes "my_lucky_biscuit"

Non-url friendly characters are replaced:
"Oh my #:*+! head!" becomes "oh_my_head"

Certain symbols are magically replaced:

"You & I" becomes "you_and_i"
"Steve @ RailsConf" becomes "steve_at_railsconf"

Bonzer!

There is currently no advanced documentation for this plugin.