CPT Archive, a WordPress Plugin
Archive widget for Custom Post Types
The CPT Archive plugin adds a modified version of the default Archives widget to let the user specify a custom post type rather than 'post', and also allows of choice or yearly or monthly archives.
This plugin requires WordPress 3.1, and the custom post type must have archives enabled, e.g., for a post type named 'press-release', $args would include 'has_archive' => 'press-release'.