Hey Giles,

auto_complete_for just relies on SomeClass.find.  Here's a really
simple couple of classes that will enable this behavior:

class ObjectMap
 def self.all_classes
   classes = []
   ObjectSpace.each_object {|o| classes << PresentedClass.new(o.name) if o.class == Class }
   classes.sort_by {|o| o.name }
 end

 def self.find(selector, find_options = {})
   name = find_options[:conditions][1][1...-1]
   all_classes.find_all { |c| c.name.downcase.include?(name.downcase) }
 end
end

class PresentedClass
 attr_reader :name

 def initialize(name)
   @name = name
 end

 def [](val)
   val == 'name' ? @name : nil
 end
end

In your controller, just do
auto_complete_for :object_map, :name

and the view should contain
text_field_with_auto_complete :object_map, :name

This is of course just a crude implementation...but you get the idea.
You can make any model searchable by providing a find method on the
class.  Then whatever objects you return must respond to both
#some_attr and ['some_attr'].

Pat