This plugin will monitor your blog looking for broken links and let you know if any are found.

Features:

> Monitors links in your posts, pages, comments, the blogroll, and custom fields (optional).
> Detects links that don’t work, missing images and redirects.
> Notifies you either via the Dashboard or by email.
> Makes broken links display differently in posts (optional).
> Prevents search engines from following broken links (optional).
> You can search and filter links by URL, anchor text and so on.
> Links can be edited directly from the plugin’s page, without manually updating each post.
> Highly configurable.