zaden Permissions 1/2/3 is a "dead" plugin now - superperms took over (aka bPermissions, PermissionsEX and PermissionsBukkit).
the ones I listed are the most updated and common ones used. PermissionsEx is the easiest to use. PermissionsBukkit is supposed to be the system used by default in Bukkit but the plugin is rarely updated. I'd suggest using pex. Don't bother even looking at essentials group manger or bperms. Thats just me.
Thanks i installed Permissionsbukkit and its too easy thanks. EDIT by Moderator: merged posts, please use the edit button instead of double posting.
Nothing a lot of people use it...I just don't like it (don't hit me haha). I said PEX because its easy.