WordPress.org

Designed for simplicity and flexibility, Simple Page Sidebars gives WordPress users, designers, and developers the ability to assign custom sidebars to individual pages--without making any template changes. Existing sidebars can also be assigned in quick edit and bulk edit modes, helping save you time.

Benefits

• No more site-wide, generic sidebars. Each page (or section) can have its own widgets.
• Complete control over sidebar names.
• Assign the same sidebar to multiple pages.
• A page's sidebar can be modified without creating a pointless revision.

Simple Page Sidebars also comes with a "Widget Area" widget for including all the widgets from one sidebar into another.