A simple plugin to make adding indexes in Rails migrations easier:

create_table :authors do |t|
  t.string :name, :index => true
  t.string :email, :index => true
  t.integer :company_id, :index => { :unique => true }
  t.text :bio
end

Install like this:

./script/plugin install http://easier-indexes.googlecode.com/svn/easier-indexes