Redirection is a WordPress plugin to manage 301 redirections, keep track of 404 errors, and generally tidy up any loose ends your site may have. This is particularly useful if you are migrating pages from an old website, or are changing the directory of your WordPress installation.

Redirection uses three core concepts: Modules, Groups and Redirects. A module consists of many groups, and each group consists of many redirections. A module determines how the redirections will be used, and a group allows you to separate redirections into logical units. A redirection represents an action performed when a particular URL is accessed.

Pricing: Free
Requirements: WordPress 2.6+
Source: http://urbangiraffe.com/plugins/redirection/