Custom Rel

By default, WordPress 2.8 puts link relation tags in the header of your posts, with the next and prev relation links pointing to the next and previous posts, chronologically. Sometimes, this is not what you want, which is where this plugin comes in. A new sidebar meta box is added to the post edit form, which lets you set the title and URL for the next and/or prev link relations. Or you can just leave them blank for the defaults WordPress behavior.

Unzip it and activate it and the meta box will be available.