User Addresses is a stand-alone address book system for Drupal. It allows individual registered users to store addresses to their address book (The most common use for this is for shipping or billing addresses).
It comes with a new menu item (in your user profile page) called 'User Addresses' that allows you to view the current addresses you have saved to your account. (Requires views).
There is also a form for adding in new addresses, as well as editing and deleting existing addresses.
It also has support for setting a 'default address'.