QuickRes is a simple app that enables HiDPI mode on your Mac, allowing you to change to lower resolutions without making things look pixelated and fuzzy. For those who own Macs with retina displays, you also gain a quick resolution switcher in your menu bar.
Previously mentioned ResolutionTab serves the same purpose, but costs $1.99. On top of that, it requires you to install a bunch of tools manually. QuickRes offers the same functionality, costs nothing and handles all of the dirty work for you. If you want to switch resolutions quickly and easily from your Mac with a retina display or just want HiDPI mode on your regular monitor, QuickRes is the way to go.