
The NES got an odd-looking redesign which simplified the cart mechanism to cut costs, which most people say was actually an improvement because the old mechanism was finnicky and prone to wearing out.
The SNES redesign was a puny thing that eliminated it's eject lever and it's RF output.
The N64's Ram Pak expansion is just an add-on, not a redesign. The N64's redesign looks like it has a dead fetus attached to it's head, with feet you can poke and cheeks that light up. Pika.
The Cube has no redesign (unless you want to count the removal of the Digital Out port). The Panasonic Q doesn't count.
Edit: The GameBoy got a redesign to become the GameBoy Pocket, which had a clearer screen, used fewer batteries, and was likely cheaper to make.
The GameBoy Color had no redesign.
The GameBoy Advance was redesigned into the SP to fix a major flaw that Nintendo doesn't admit ever really existed, and it didn't use batteries anymore. (The design is cool, but the old one wasn't exactly lame.)
The GameBoy Advance was redesigned again into the micro in an attempt to make cost-cutting cool.
And the GBA SP was "upgraded" to use a better screen.
Now the DS is being redesigned for it's appearance, it's weight, and also apparently because lately Nintendo's practically itching to upgrade their screens every time they see a newer version.