Hello, I would like to suggest a simple plugin for PVP. This plugin is set to drop a player head when a player is killed, it will only drop though .5% of the time, and it will only drop when a player is killed by another player. Nothing else will cause the head to drop. It can also be set up to drop mob heads when mobs are killed, with a whole different set of percentages. This could also be included in a VIP package, where they can get the head if their own, or possibly a friend. I have tried this out before and it does not seem to mess with any other plugins.
http://www.curse.com/server-mods/minecraft/player-heads
http://dev.bukkit.org/server-mods/player-heads/
Note: It will drop the head of the player, with the players skin on at the time. It will NOT be the default Steve head, that is unless the player is wearing the Steve skin.
Note #2: The drop rates are all adjustable, and it comes with a set of commands (Op only) that can spawn in player heads without them needing to be killed. All drop rates are adjusted in the config files.