1. GameWatch - The beginning of handheld video gaming.
2. Atari2600 - The beginning of home console.
3. Nintendo - A lot of good games started from here (Zelda, Metroid, etc.)
4. Sega Genesis - The beginning of 16-bit gaming, and broke a lot of 8-bit limitations. Sonic platforming technology was such a huge improvement over Mario, for example. A lot of games that were only available on the arcades were portable to this console.
5. Xbox360 + Kinect - Tough choices between all the modern consoles (N64, PS, PS2, PS3, Cube, Wii, Xbox), but I think Xbox with Kinect wins. The need of not using a controller spawns new genres of video games.