Game Boy
The Game Boy, Nintendo's flagship handheld console, was first released in 1989, and even today, is considered the best selling handheld console of all time.
The console's first incarnation was large and white, with a monotone dot matrix screen and stereo sound that rivaled larger consoles.
In 1998, the Game Boy Color was released. It was slightly smaller than the original Game Boy, and arrived in a wide array of colores...but the biggest change was in the graphics display, which could now display colors instead of black and white.
The current form of the Game Boy, the Game Boy Advance, was released in 2001. Not only did it look dramatically different (a semi trapezoidal shape compared to the square shape of the original Game Boy and Game Boy Color), but it also contained a powerfull processor, allowing it to display SNES caliber graphics and even play voices.