Display Maestro gives you full control over attached displays, allowing the usage of all available resolutions and bit depths. This is done by ignoring the operating system setting of hiding potentially unsafe resolutions.
I do not have a Retina-enabled Mac to test this on; but on my MacBook Air, Display Maestro offers a few resolutions that are not available in Apple’s built-in Display preferences. The app sits quietly in the menubar and allows you to switch resolutions with the click of the mouse. On some systems, it will even allow you to switch to 256-color depth—perfect for those older games that can’t switch automatically.
If you have the need to view your screen in numerous resolutions, Display Maestro is a handy utility to have at only $4.95. A 15-day downloadable demo is available.