Download source code for all RailsCasts episodes. You may want to cd into an empty directory first.

railscasts_episodes.rb

require "rubygems"
require "octokit" # gem install octokit

1.upto(5) do |page|
  Octokit.repositories("railscasts", page: page, per_page: 100).each do |repo|
    system "git clone git://github.com/railscasts/#{repo.name}"
  end
end

I've slightly changed the script to clone only repositories which have not been cloned yet in this gist https://gist.github.com/gawlista/4978183 or this Ruby project https://github.com/gawlista/railscasts-episodes if you like.