MinecraftHeads is a unique head generation plugin that addresses two main issues that arise when storing player head by username while also creating a clean organized user interface. This plugin downloads an updated list of heads via an updatable Google spreadsheet, indexes them into categories, and allows users to select and search for their desired heads. Inspired by the subreddit /r/MinecraftHeads, this plugin keeps track of whether or not heads are "safe" (an indicator of its possiblity to change in the future).
Download: http://dev.bukkit.org/bukkit-plugins/minecraft-heads/