Multiple sortable images using Paperclip. Example using a Page model.

_form.html.erb

<%= f.error_messages %>
<p>
  <%= f.label :name %><br />
  <%= f.text_field :name %>
</p>
<p>
  <%= f.label :permalink %><br />
  <%= f.text_field :permalink %>
</p>
<p>
  <%= f.label :content %><br />
  <%= f.text_area :content %>
</p>
<h2>Images</h2>
<div id="image_listing_wrapper" class='listing_wrapper'>
  <%= render :partial => 'shared/images', :locals => {:viewable => @page, :f => f} -%>
</div>
<%= render :partial => 'shared/image_actions', :locals => {:viewable => @page, :f => f} -%>
<h2>Documents</h2>
<div id="document_listing_wrapper" class="listing_wrapper">
  <%= render :partial => 'shared/documents', :locals => {:viewable => @page, :f => f} -%>
</div>
<%= render :partial => 'shared/document_actions', :locals => {:viewable => @page, :f => f} -%>

asset.rb

class Asset < ActiveRecord::Base
  belongs_to :viewable, :polymorphic => true
  acts_as_list :scope => :viewable
end

edit.html.erb

<h1>Editing page</h1>
<% form_for @page, :html => { :multipart => true, :method => :put } do |f| %>
  <%= render :partial => 'form', :locals => { :f => f } %>
  <%= render :partial => 'shared/edit_resource_links', :locals => { :collection_url => pages_path } %>
<% end %>

<!-- _edit_resource_links.html.erb -->
<!-- <%= submit_tag "Update", :class => "button" %> or <%= link_to "Cancel", collection_url %> -->

image.rb

class Image < Asset
  has_attached_file :file,
                    :styles => { :thumb => '75x75#', :small => '250x250>', :medium => '475x475>', :full => '792x792>' },
                    :default_style => :medium
 
  validates_attachment_content_type :file, :content_type => ['image/jpg', 'image/jpeg', 'image/pjpeg', 'image/png', 'image/x-png', 'image/gif', 'image/tiff']
end

images_controller.rb

class ImagesController < ApplicationController
 
  # GET /images/new
  # GET /images/new.xml
  def new
    @image = Image.new
 
    respond_to do |format|
      format.html # new.html.erb
      format.xml { render :xml => @image }
    end
  end
 
  # POST /images
  # POST /images.xml
  def create
    @image = Image.new(params[:image])
 
    respond_to do |format|
      if @image.save
        flash[:notice] = 'Image was successfully created.'
        format.html { redirect_to(@image) }
        format.xml { render :xml => @image, :status => :created, :location => @image }
      else
        format.html { render :action => "new" }
        format.xml { render :xml => @image.errors, :status => :unprocessable_entity }
      end
    end
  end
 
  # DELETE /images/1
  # DELETE /images/1.xml
  def destroy
    @image = Image.find(params[:id])
    @viewable = @image.viewable
    @image.destroy
 
    respond_to do |format|
      format.html do
        flash[:notice] = nil
        render :partial => '/shared/images', :locals => {:viewable => @viewable}
      end
      format.xml { head :ok }
    end
  end
end

new.html.erb

<h1>New page</h1>
 
<% form_for @page, :html => { :multipart => true } do |f| %>
  <%= render :partial => 'form', :locals => { :f => f } %>
  <%= render :partial => 'shared/new_resource_links', :locals => { :collection_url => pages_path } %>
<% end %>

<!-- _new_resource_links.html.erb -->
<!-- <%= submit_tag "Create", :class => "button" %> or <%= link_to "Cancel", collection_url %> -->

page.rb

class Page < ActiveRecord::Base
  has_many :images, :as => :viewable, :order => :position, :dependent => :destroy

  validates_presence_of :name, :permalink
end

pages_controller.rb

class PagesController < ApplicationController
  after_filter :set_image, :only => [:create, :update]
 
  # GET /pages
  # GET /pages.xml
  def index
    @pages = Page.all
 
    respond_to do |format|
      format.html # index.html.erb
      format.xml { render :xml => @pages }
    end
  end
 
  # GET /pages/1
  # GET /pages/1.xml
  def show
    if params[:permalink]
      @page = Page.find_by_permalink(params[:permalink])
      raise ActiveRecord::RecordNotFound, "Page not found." if @page.nil?
      respond_to do |format|
        format.html # show.html.erb
        format.xml { render :xml => @page }
      end
    else
      @page = Page.find(params[:id])
      respond_to do |format|
        format.html # show.html.erb
        format.xml { render :xml => @page }
      end
    end
  end
 
  # GET /pages/new
  # GET /pages/new.xml
  def new
    @page = Page.new
 
    respond_to do |format|
      format.html # new.html.erb
      format.xml { render :xml => @page }
    end
  end
 
  # GET /pages/1/edit
  def edit
    @page = Page.find(params[:id])
  end
 
  # POST /pages
  # POST /pages.xml
  def create
    @page = Page.new(params[:page])
 
    respond_to do |format|
      if @page.save
        flash[:notice] = 'Page was successfully created.'
        format.html { redirect_to edit_page_path(@page) }
        format.xml { render :xml => @page, :status => :created, :location => @page }
      else
        format.html { render :action => "new" }
        format.xml { render :xml => @page.errors, :status => :unprocessable_entity }
      end
    end
  end
 
  # PUT /pages/1
  # PUT /pages/1.xml
  def update
    @page = Page.find(params[:id])
 
    respond_to do |format|
      if @page.update_attributes(params[:page])
        flash[:notice] = 'Page was successfully updated.'
        format.html { redirect_to edit_page_path(@page) }
        format.xml { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml { render :xml => @page.errors, :status => :unprocessable_entity }
      end
    end
  end
 
  # DELETE /pages/1
  # DELETE /pages/1.xml
  def destroy
    @page = Page.find(params[:id])
    @page.destroy
 
    respond_to do |format|
      format.html { redirect_to(pages_url) }
      format.xml { head :ok }
    end
  end
  
  private
    def set_image
      return unless params[:image]
      return if params[:image][:file].blank?
      image = Image.create params[:image] if params[:image]
      @page.images << image
    end
end

schema.rb

ActiveRecord::Schema.define(:version => 20090317175259) do
 
  create_table "assets", :force => true do |t|
    t.integer "viewable_id"
    t.string "viewable_type"
    t.string "file_content_type"
    t.string "file_file_name"
    t.integer "file_file_size"
    t.integer "position"
    t.string "type"
    t.datetime "file_updated_at"
  end
 
  create_table "pages", :force => true do |t|
    t.string "name"
    t.string "permalink"
    t.text "content"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer "viewable_id"
  end

end

show.html.erb

<ul id="image_listing">
  <% @page.images.each do |image| %>
    <li>
      <%= image_tag image.file.url %>
    </li>
  <% end %>
</ul>