Well this kinda came out of nowhere. I guess it's not too surprising since i'm guessing there aren't that many people still using the online services in these games but Nintendo could have given us some kind of heads up before pulling the plug.
Nintendo has announced that as of May 20th, online play, matchmaking and leaderboards will be shut off for many Wii, DS and DSi games. Online play of course will continue for Wii-U and 3DS.
I had a lot of fun playing Mario Kart and Super Smash Brothers online so it's kinda sad to see that these games will be going offline for good.
Here is a full list of games that will be affected.
Nintendo DS
100 Classic Books
Animal Crossing: Wild World
Advance Wars: Days of Ruin
Clubhouse Games
Custom Robo Arena
Diddy Kong Racing DS
Dragon Quest IX: Sentinels of the Starry Skies
Dragon Quest Monsters: Joker 2
Fire Emblem: Shadow Dragon
Fossil Fighters: Champions
Legend of Zelda: Phantom Hourglass
Mario Kart DS
Mario vs. Donkey Kong 2: March of the Minis
Mario vs. Donkey Kong: Mini-Land Mayhem
Metroid Prime Hunters
Personal Trainer: Walking
Picross 3D
Picross DS
Planet Puzzle League
Pokémon Black Version
Pokémon Black Version 2
Pokémon Diamond Version
Pokémon HeartGold Version
Pokémon Mystery Dungeon: Explorers of Darkness
Pokémon Mystery Dungeon: Explorers of Sky
Pokémon Mystery Dungeon: Explorers of Time
Pokémon Pearl Version
Pokémon Platinum Version
Pokémon Ranger: Guardian Signs
Pokémon Ranger: Shadows of Almia
Pokémon SoulSilver Version
Pokémon White Version
Pokémon White Version 2
Professor Layton and the Curious Village
Professor Layton and the Diabolical Box
Professor Layton and the Last Specter
Professor Layton and the Unwound Future
Star Fox Command
Style Savvy
Tenchu: Dark Secret
Tetris DS
WarioWare DIY
Nintendo DSiWare
Mario vs. Donkey Kong: Minis March Again!
Metal Torrent
Number Battle
Wii
Animal Crossing: City Life
Battalion Wars 2
Endless Ocean
Endless Ocean 2: Adventures of the Deep
Excitebots: Trick Racing
Fortune Street
Mario Kart Wii
Mario Sports Mix
Mario Strikers Charged
Pokémon Battle Revolution
Samurai Warriors 3
Sin & Punishment: Star Successor
Super Smash Brothers Brawl
Wii Music*
WiiWare
Dr. Mario Online RX
Excitebike: World Rally
LONPOS
Maboshi's Arcade
My Pokémon Ranch
ThruSpace
WarioWare DIY
Other
Wii Speak**
Wii Speak Channel**
(*) Services that require Internet communication ended on June 28, 2013.
(**) As Nintendo Wi-Fi Connection is required to use this title, it is no longer functional