Display Widgets SEO Plus is a WordPress plugin that gives you control over the circumstances where a widget will be displayed. It’s an alternative to building multiple sidebars for pages, with Display Widgets SEO Plus you put all of your widgets in the default sidebar and then choose on a widget by widget basis exactly where that widget will be displayed.
WP Custom Sidebars is as WordPress plugin that allows you to replace the any default sidebar with one specific for that page or post etc.
Woosidebars is a plugin that allows you to replace sidebars with those of your own creation on specific pages throughout your WordPress site, technically you could have a different sidebar per page.
Content Aware Sidebars is a WordPress plugin that allows you to create page specific sidebars that replace or merge with the default theme sidebars. The plugin comes with built in support for BuddyPress pages. Content Aware Sidebars has been created for those sites that want to create a unique look on some or all pages by allowing for page specific sidebar content.
