HappyMapper is John Nunemaker's attempt at "making XML fun again" for Rubyists by providing an object to XML mapping library with a succinct syntax. Essentially, you can use HappyMapper to rapidly turn XML into Ruby objects - even nesting them inside and referring to each other. This is powerful stuff. To install, just gem install happymapper

John's own examples are powerful demonstrations of how it works, so check them out. The first is parsing the XML returned from Twitter. The statues and associated users in that XML can be processed (with the relationship maintained) with the following code:

class User
  include HappyMapper

  element :id, Integer
  element :name, String
  element :screen_name, String
  element :location, String
  element :description, String
  element :profile_image_url, String
  element :url, String
  element :protected, Boolean
  element :followers_count, Integer
end

class Status
  include HappyMapper

  element :id, Integer
  element :text, String
  element :created_at, Time
  element :source, String
  element :truncated, Boolean
  element :in_reply_to_status_id, Integer
  element :in_reply_to_user_id, Integer
  element :favorited, Boolean
  has_one :user, User
end

statuses = Status.parse(xml_string)
statuses.each do |status|
  puts status.user.name, status.user.screen_name, status.text, status.source, ''
end

Added: Or.. how about a similar library that doesn't require naming the elements to work (but then lacks typecasting)? Check out xml-object by Jordi Bunster.