When WordPress 2.6 was released several months ago, one of the innovations that it provided was that of post revisions. It can be a real pain when you delete a large portion of your blog post and then you accidentally save it. In previous iterations, all of that work may have quite easily been lost. With revisions, you can revert back to an older copy of your posts and pages.
This is a very handy feature and can be a real lifesaver, but it can also create quite a burden on your database and it can also make for quite the messy situation. A plugin has been created by Dion Hulse that addresses this very issue.
Going through the settings, you can completely control how the revision process works on your blog. You can limit the number of revisions that are saved for each page or post. You can also delete specific revisions after the fact, thus clearing out some of that superfluous and duplicate data. Alternatively, you can choose to disable revisions altogether or control the number of revisions on a per-post basis.
For more information and screenshots, as well as a link to the download, check out Revision Control in the official WordPress plugin directory.