Nintendo is no longer supporting its Wi-Fi Connection service as of today, marking the end of online functionality for Wii, DS, and DSi games -- but, notably, not the end of the Wii Shop Channel, DSi Shop, and video services. You can still make use of those.
We knew this closure was coming but these things sure have a way of sneaking up on you. Nintendo has a list of affected titles over here, featuring the likes of Animal Crossing: Wild World and City Life, Mario Kart DS and Wii, Dragon Quest IX, Super Smash Bros Brawl, Endless Ocean, and Pokémon games leading up to the not-very-old-at-all Black/White Version 2.
Lot of casualties. No more Wii Speak, either. Even for games of lesser quality, it's often sad to see a part of them (or the whole thing, in the case of MMOs) "die" when it's inevitably no longer practical to support the limited audience making use of online play. Time keeps on slipping.