Use plugins.bukkit.org and search for invisibility,poof,vanish or type poof in the top right hand corner in the search bar. I will not give you the direct link, people need to learn to use the search feature.
People really don't know how to search . Maybe you should try a different query that is similar to poof. Cough, cough, VANISH, cough cough. I won't directly link you to it like above, but it should take literally 2 seconds of searching to find it.
