Document Links Widget plugin by Lorie Ransom displays all attachments from the WordPress database in the Document Links admin panel, divided into four categories: PDF, Word Docs, ZIP archives and Other. Within the admin panel, you can select which documents you would like to appear, then configure the Document Links Widget and drag it into the sidebar.
You can place as many Document Links Widgets in the sidebar as you like which allows you to show different categories under different titles in the sidebar if you wish.
Download: http://wordpress.org/extend/plugins/document-links-widget