The bukkit plugin that has Optional PvP is called WAR. However there has been many complains about the PVP at the server and Prev stating to reduce PVP to specail areas. Please keep in mind that all players recieve the same equipment when they join a war zone and when they depart. Overall the most common thing would be the warhub, also from the point you can certainy teleport immediately to a warzone of your choice. In conclusion this is some basic information about bukkit plugin that has optional PVP.