user_grid.rb

module Netzke
  class UserGrid < Basepack::GridPanel
    def default_config
      config = super
      config.merge({
          :model => 'User',
          :columns => [:first_name, :name, :email, :login,
            {:name => :salutation, :editor => { :xtype => "combo", :store => [['mr', 'Herr'], ['mrs', 'Frau']]  }},
            :title, :confirmed_at, :locked_at]
        })
    end
  end
end

You may want to override GridPanel#default_fields_for_forms like this:

def default_fields_for_forms
  orig_fields = super.dup
  orig_fields.detect{ |f| f[:name] == "salutation" }.merge!(:xtype => "combo", :store => [['mr', 'Herr'], ['mrs', 'Frau']])
  orig_fields
end

default_fields_for_forms may even return an arbitrary layout of fields that will be common for all forms that the grid uses.