There is the Wiikey, Wiinja Deluxe, and Cyclowiz.
Also, these are first generation modchips, which can only be applied to a Wii motherboard model D2A and D2B. If you're gonna buy your Wii now, you'll most probably get the D2C motherboard, and these modchips won't work on it. The only modchip that works on the D2C motherboard is the D2CKey, which is a 31-wire install. Also, its always good to buy a modchip that can be updated just like the Wiikey, Wiinja Deluxe, and the Cyclowiz as newer protection by Nintendo can be beat like this, just like they did it with Super Mario Galaxy.
Unfortunately, the D2CKey CANNOT be updated, which means you're gonna get stuck if Nintendo comes up with some new kind of protection for preventing backups to boot, which might need a modchip update. It was just PLAIN LUCK that the Wii's fitted with the D2CKey were able to play Super Mario Galaxy. Older generation modchips required an update.
You might wanna wait up for a while and see if a newer modchip becomes available for the D2C motherboard, which can be updated via DVD
Edit: If you already have a Wii, you can check which motherboard your Wii has by putting your serial number in this website.
Nintendo-Scene Wii Serial Tracker
If you're lucky enough to have a D2A or a D2B motherboard, then you can get is modded with any of the first generation modchips, which just require a 5-wire install
Hope this helps