Cyberbike Magnetic Edition
The Cyberbike Magnetic Edition is a bike peripheral for the Wii, made by Big Ben Interactive. At the time of the release, it actually costed more than the Wii itself. The bike plugs into the GameCube controller slot; you can use the accessory with games that support the GameCube controller like Mario Kart Wii, and it's not supported with the Wii Family Edition.
It was released in the US and Europe, and bundled with a game called Cyberbike Cycling Sports (which makes the game rare, at least we know for the US version of the game).
On Amazon, the accessory got mixed reviews. Somehow, the bike got a sequel called Cyberbike 2 for the PS3, with a game called Cyberbike Cycling Sports 2.