Sega was quite crazy too. From the top of my head:

* The Megadrive plus MegaCD plus 32X, affectionately called "The Tower of Power". I have one and it is quite a hefty beast.

* Sonic & Knuckles with its lock-on technology that allowed plugin Sonic 3 (or Sonic 2) to form the full game.

* Virtua Racing and its SVP chip, Sega's answer to the SuperFX.

* The Saturn and its extension cartridges that provided additional RAM.

* The Dreamcast and its VMU.