ImmortalNpc

With this plugin you don't need to worry about Villagers on your server. If player don't have required permission (immortalnpc.ignore) he can't hurt villagers. Maybe you will can add Villagers to whitelist, other npcs will be dead :)
If you try to hurt villager, you will see message like this on screenshoot. Please leave a comment if you found bug, or know what would I add to this plugin.

Latest Version: 1.1
Working with CraftBukkit: 1.7.2

Permissions:

• immortalnpc.attack - Attack villagers
  
• immortalnpc.trade - Trade with villagers
  

Installation:

• Download ImmortalNpc.jar
  
• Put it into plugins/
  
• Run the server
  
• Done!
  

Youtube tutorial (Polish):
http://www.youtube.com/watch?v=MiTs146YCTQ