Everybody knows the griefer that destroys or places blocks, but PvP griefing is a big issue too. They prevent players from exploring the wilderness and prevents newcomers from enjoying the server. Even setting up non-PvP areas like cities does not fix the problem. So what does fix the problem? This plugin.
This plugin lets players turn on PvP for themselves. Once two combatants turn on PvP, they can battle it out. Otherwise, players cannot be damaged by others. No more sneak attacks from griefers who only want to make your life miserable. Players will never feel outmatched again.
This plugin is currently going under some MAJOR code changes and feature updates. Feel free to get the source here or check out an older version at this forum thread, but I cannot guarantee that it will work properly. I am close to having v2.0 finished, so check out here for my release jar.