This works with Rails 2.3 and the rails-2.3 branch of ActiveScaffold.

Enhancements:
The following exports are supported:
Excel
Enhanced XML To File (uses XSL Stylesheet)
Enhanced XML
Raw XML
CSV
Stylesheet (XSL stylesheet. Used by Enhanced XML To File) 

Raw XML is a rails "to_xml" which dumps the db/model data i.e. just the ids for any associations. 
All others export what you see in the list i.e. real association data. 
For plural associations, all records are output - not just the first 3 like you see in an AS list. 

Gems required:
fastercsv
surpass (for Excel export)

Features from http://code.google.com/p/activescaffoldexport/wiki/Features

Introduction

Active Scaffold plugin with some configuration options and a FasterCSV implementation (which can be easily overridden)
Details

Actual CSV export implementation can be easily overridden via a template override

   1. Built in CSV export implementation uses FasterCSV (must be installed via GEM)
   2. Several customization options available at both global and controller config layer including: 

    * show_form - skip customization form and just automatically export from action link
    * allow_full_download - allow user to only export the current page or all AR items
    * force_quotes - Always wrap all fields in quotes (using FCSV feature)
    * default_full_download - Whether page or full download is the default option in show_export form
    * default_delimiter - defaults to , (different from the prior code's default of ;)
    * default_skip_header - default for the omit header form option
    * default_deselected_columns - list of columns that the user can export but aren't selected by default 

Usage

Add the export action to your controller:

  active_scaffold :people do |c|
    c.actions.add :export
    c.export.columns = [ :id, :name, :birth_date ]
    c.export.default_deselected_columns = [ :birth_date ]
    c.export.default_delimiter = ';'
    c.export.force_quotes = true
  end
  
or for all controllers:

class ApplicationController < ActionController::Base
  ActiveScaffold.set_defaults do |config|
    config.actions.add :export
  end
end

The output filename is controller_date.format e.g. people_2010-04-14.csv
You can customize this by overriding #export_file (everything except stylesheets) or #export_file_name(:format) in your controller   
e.g.
  def export_file
    "output"
  end
would give you output.csv, output.xls, etc (but keep the stylesheet as people.xsl)

You can override the background color in the stylesheet by overriding #bgcolor
e.g
  def bgcolor
    "#AADDAA"
  end

I have renamed the old activescaffoldexport plugin to follow the same pattern as the other ActiveScaffold related plugins.