SwitchRes is an utility built around a Control Panel and an Extension. It will allow you to control and automate the resolutions of all your monitors. It is distributed with a Control Strip Module and a Contextual Menu Item, so that it's always available everywhere.
SwitchRes is completely configurable. You can define which resolutions are really accessible, and which will require a confirmation.
This software's licence is Shareware - Unlimited, which means that the current version is free of charge for now; no time or feature restrictions in this version.