Multiplayer matchmaking service GameSpy will be closing down on  May 31, leaving games like Battlefield Bad Company 2, Civ 4 and Crysis, to name a few, without proper multiplayer support. While many developers and publishers have already confirmed that replacement services are being prepared, a lot of games are still unaccounted for.

The good folks at /r/Game have made a list of titles affected by Gamespy's shutdown, so scroll down if you're playing any games using the service. Bear in mind this is an unofficial list and any info is subject to change.

Affected

   Arma
   Arma: Cold War Assault
   Arma 2
   Arma 2: Free
   Borderlands
   Dungeon Defenders [PS3/Non-Steam]
   Halo: Combat Evolved
   Saints Row 2
   Star Wars Battlefront
   Star Wars Battlefront 2
   Stronghold 2
   Stronghold Legends
   Take On Helicopters

Status Unknown

   Alien vs Predator 2
   Battlefield 1942
   Battlefield 2
   Battlefield 2142
   Battlefield Bad Company 2
   Battlefield Vietnam
   Call of Juarez
   Call of Juarez Bound in Blood
   Civilization III
   Civilization IV
   Commandos: Behind Enemy Lines
   Commandos: Behind the Call of Duty
   Crysis
   Crysis Warhead
   Crysis Wars
   Far Cry
   Jagged Alliance 2
   Medal of Honor: Pacific Assault
   Medal of Honor: Allied Assault
   Medieval Total War
   Medieval Total War 2
   Need For Speed: Hot Pursuit
   Need For Speed: Hot Pursuit 2
   Postal 2
   Red Dead Redemption
   Shogun Total War
   SWAT 4
   Titan Quest
   Tom Clancy's Ghost Recon
   Tom Clancy's Ghost Recon Advanced Warfighter
   Tom Clancy's Ghost Recon Advanced Warfighter 2
   Tom Clancy's HAWX
   Tom Clancy's Splinter Cell Chaos Theory
   Tom Clancy's Splinter Cell Double Agent
   Two Worlds
   Two Worlds 2
   Warhammer 40K: Dawn of War
   Warhammer 40K: Dark Crusade
   Warhammer 40K: Soulstorm
   Warhammer 40K: Winter Assault

Probably Unaffected

   Alien vs Predator (Classic)
   Call of Duty
   Call of Duty United Offense
   Call of Duty 2
   Commandos 2
   Commandos 3
   Jagged Alliance
   Hexen
   Hexen 2
   Quake 2
   Quake 3
   Quake 4
   Soldier of Fortune
   Soldier of Fortune 2
   SWAT 2
   SWAT 3
   Unreal Tournament
   Unreal Gold
   Unreal 2

Unaffected

   Arma 2: Operation Arrowhead
   Arma 3
   Company of Heroes
   Multiwinia
   Street Fighter 3: 3rd Strike Online Edition
   Stronghold HD
   Stronghold Crusader HD