The 3DS isn't the first Nintendo console to enter the public consciousness with a name that's never actually used. Plenty of other machines have also been revealed with names never destined for a retail shelf.
Yes, we know, Nintendo isn't the only company to do this. Pretty much anyone and everyone involved in making anything uses code names for products and technology that are in development. But for some reason, probably due to the company's loyal, rabid fanbase - not to mention the fact the code names were often better than the final title - Nintendo's seem to capture the imagination, and live long after many actual product names have come and gone.
PROJECT REALITY - Project Reality was the code name for the console that would become the Nintendo 64. And the Ultra 64. But then just the Nintendo 64.
DOLPHIN - Conjuring images of tricks-for-fish and a classic Sega game, Dolphin was the working title for the Nintendo GameCube. In a cute touch, the console's GPU is called "Flipper".
DS - It's a part of gaming vernacular now, but it's often overlooked that "DS" (Developer System, or Dual Screen) was originally a concept title for the handheld, not its final branding. What's more, it was the third code name the console went through, having first been called Iris, then Nitro.
REVOLUTION - Probably the most famous of the bunch, Nintendo originally unveiled the Wii as the "Revolution", a name that seemed to fit perfectly with what the company was doing with the machine. At least part of the initial furore over the console's re-branding was down to the fact "Wii" not only sounded a little stupid, but that it wasn't anywhere ner as good a name as Revolution. Or the Rev, as it would no doubt have been abbreviated to.
3DS - Like we've said, the 3DS is a working title for Nintendo's 3D handheld, and while there's a chance it might also be the final name (it has a precedent with the DS), there's also scope for it to be something a little more...imaginative.
UPDATE - Sharp-eyed reader NotTheGuy points out that these code names live on in the ID numbers given to Nintendo products. Resident Evil 4 on Wii, for example, has the code number RVL P RB4, the "RVL" short for "Revolution". Same for the GameCube, Star Fox Adventures on GameCube? DOL-P-GSA, the "DOL" short for "Dolphin".