OpenEmu (free) is console and arcade game emulator for OS X. It emulates Game Boy, Game Boy Advance, Game Gear, NeoGeo Pocket, Nintendo (NES), Nintendo DS, Sega 32X, Sega Genesis, Sega Master System, Super Nintendo (SNES), TurboGrafx-16 and VirtualBoy.
One very neat feature of OpenEmu is support for different controllers. Some of the controllers it supports include PS3, PS4, Xbox 360 and Nintendo Wiimote (full list). This will improve gaming experience if you have one of the supported controllers.
OpenEmu also organises your games into an easy to use library. It also allows you to create your own game collections.