permission plugin. http://forums.bukkit.org/threads/in...sions-3-1-6-the-plugin-of-tomorrow-935.18430/
Don't listen to this noob. bPermissions is my recommendation http://dev.bukkit.org/server-mods/bpermissions/ Lots of work is being done all the time to make it even better!
O no its this @codename_B noob (shamelessly plugging his own plugin XD ) anyways on a serious note permissions 3.1.6 WAS the best now it looks like PEX is taking over as the current best permissions (but "best" is all perspective) just look at all your options and decide