Big Brother was initially created by tkelly910 , but is now maintained by N3X15.If you've ever had the misfortune of waking up to an entire server griefed, and not a greifer in sight, then this plugin is for you. Big Brother hooks up into a SQL database and records each and every action taken on each and every block.
Using special in-game tools, you can then "audit" edits to your world. You can see who destroyed what and when. It even shows you multiple edits back, so you can see if someone broke an item, and then put it back. When you want to revert all the changes someone made, you can simply rollback all their edits.
Big Brother requires the use of CraftBukkit, and is by no means easy to install. You have to have access to a SQL server, and some basic knowledge of how SQL works. If you think you can manage that, then head on over to the Bukkit page for Big Brother and learn how to set it up.