gistfile1.rb

# helpers/application_helper.rb
module ApplicationHelper 
  def setup_user(user)
    user.build_account unless user.account
    user 
  end 
end

# app/models/account_owner.rb
class AccountOwner < ActiveRecord::Base
  has_one :account, :validate => true
  
  # Include default devise modules. Others available are:
  devise :database_authenticatable, :registerable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :account_attributes
  
  accepts_nested_attributes_for :account
end

# app/models/account.rb
class Account < ActiveRecord::Base
  belongs_to :account_owner
  validates_presence_of :name
  attr_accessible :name
end

# Devise Registration Form (modified)

<h2>Sign up</h2>

<%= form_for(setup_user(resource), :as => resource_name, :url => registration_path(resource_name)) do |f| %>
  <%= devise_error_messages! %>
  
  <p><%= f.label :email %><br />
  <%= f.text_field :email %></p>

  <p><%= f.label :password %><br />
  <%= f.password_field :password %></p>

  <p><%= f.label :password_confirmation %><br />
  <%= f.password_field :password_confirmation %></p>
  
  <%= f.fields_for :account do |af| %>
  <p><%= af.label :name %><br />
  <%= af.text_field :name %></p>
  <% end %>

  <p><%= f.submit "Sign up" %></p>
<% end %>

<%= render :partial => "devise/shared/links" %>