TaxFreeRegion is a Bukkit plugin which enables you to define regions where a user who enters that region gets different permissions. You can black- and whiltelist specific commands (not only basic commands - the black-/whiltelist checks the whole command with all parameters). Additionally you can control what the plugin does when a player enters or leaves a region (execute commands, change the inventory, ...). The plugin also offers certain protection options which ensure that a player cannot abuse extended rights which he got inside the region.
For further information visit: http://dev.bukkit.org/server-mods/taxfreeregion/