This isn’t a new plug-in, but it’s new to me and I love it!
I recently converted one of my sites from a custom CMS to WordPress mu. I manually 301 redirected some of the popular pages, but decided to let the rest of them die off. However, I just installed the Redirection plug-in
and I’m cleaning it up like magic!
It automatically logs 404 errors on the site, then lets you turn that 404 into a 301 redirect with a single click. I point the 404 to the comparable page on the new blog, and things are quickly falling into place. I should see much less of a traffic drop-off now that I’m using this.
It won’t be a terribly useful plug-in for most blogs, but if you’re converting any site to use WordPress, this is a great way to get things tidied up.