Japanese Release Date:  September 28th, 2006
American Release Date:  April 22nd, 2007

Overview:  In the first installments of the fourth generation, players take control of a trainer growing up in the Shinou region.  There, he or she will face off against the Ginga-Dan while trying to obtain the region's 107 pokemon.  New features added to this set of games is connectivity to the previous generation's games, Wi-Fi connectability, and a number of aesthetic changes.  

Changes:  A glitch that made you get stuck in a wall while fighting the Four Emperors and enabled you to capture a Darkrai has been removed from the American version.

Also, several references to the animated movies that existed in the Japanese version were overlooked by the English translators.  Among those references:

Hitomi, from The Sky-Splitting Visitor, Deoxys, shows up on Route 224 with a Metagross.  In the English version, this trainer, who should have been named Rebecca, has been renamed Jamie.

Butler and Dianne, from The Seven Nights' Star of Wishing, Jiraachi, show up on Route 229.  Butler has a Samayoru and Bohmander while Dianne has a Guraena and a Kirlia.  In the English version, they were renamed Felix and Dana.

Special thanks to Maxim for pointing these cameos out in this thread on Bulbagarden.

Official Pocket Monsters Diamond  & Pocket Monsters Pearl Japanese Site

Official Pokémon Diamond Version & Pokémon Pearl Version American Site

Japanese Release Date:  September 13th, 2007
American Release Date:  April 20th, 2008

Overview:  Players once again assume the role of a person who wakes up one day and finds that he's become a pokemon.  After joining the Pukurin Guild, you set out to keep the "Cog of Time," a treasure capable of stopping time, from falling into the wrong hands!  The game features 490 pokemon, including those introduced in the Diamond & Pearl games.  WiFi capabilities are included.  

Changes:  N/A

Japanese Release Date:  March 20th, 2008
American Release Date:  November 10th, 2008

Overview:  This is the first sequel to the popular Pokemon Ranger spin-off series!  Players choose either a boy or a girl students from Ranger School to complete the school's training program and become full-fledged Rangers!  Then, players will be able to participate in a number of missions in the Almia region.  The game features pokemon from the Diamond & Pearl games and features WiFi capabilities.

Changes:  N/A

Japanese Release Date:  September 13th, 2008
American Release Date:  March 22nd, 2009

Overview:  Pocket Monsters Platinum is the update to the Diamond & Pearl games.  New features include a new outfit for the protagonists, additional plot elements that center around Giratina, a new area known as the Torn World, and new formes for pokemon like Giratina and Shami.

Changes:  In the European versions of the game, the slot machines were taken out of the Game Corner.

Japanese Release Date:  April 18th, 2009
American Release Date:  October 12th, 2009

Overview:  Sky Rescue Team is an update to the previously released Time Rescue Team and  Darkness Rescue Team the same way that Platinum is an update to Diamond & Pearl.  Updates include new selectable player characters and a new episode involving a Juptoru who's traveling from the future.

Changes:  N/A

Japanese Release Date:  September 12th, 2009
American Release Date:  March 14th, 2010

Overview:  HeartGold and SoulSilver are remakes of the second generation of games, Pocket Monsters Gold and Pocket Monsters Silver.  The games feature graphics similar to the fourth generation games and contain additions such as a completely intact Kanto region, a series of events known as Pokethlon, and new characters and scenarios.  The games also come packaged with a pedometer called the PokeWalker that allows players to earn experience for their pokemon even when they're not playing.

Changes:  The slot machines in the Game Corner have been removed for the international releases.  The slots have been replaced with a new game called "Voltorb Flip."

Japanese Release Date:  March 6th, 2010
American Release Date:  October 4th, 2010

Overview:  In this third game in the Pokemon Ranger series, you play as a Pokemon Ranger in the island region of Oblivia.  This time around, Rangers are able to summon pokemon in battle by drawing specific symbols on their DS' touch screen.  Up to four players may join forces in a cooperative play mode.

Changes:  N/A

Japanese Release Date:  September 18th, 2010
American Release Date:  March 6th, 2011

Overview:  The fifth generation!  You take control of a young trainer as he or she travels through the Isshu Region, fighting the Plasma-Dan while trying to obtain the region's 156 pokemon.   The games boast fully animated battles, three-on-three battles, combination techniques, and the most intricate plotline to a main series game yet!

Changes:  N/A

Japanese Release Date:  April 21st, 2011
American Release Date:  N/A

Overview:  This "typing adventure game" asks players to conduct pokemon battles by entering the names of the pokemon as they appear on the screen.  Over 400 pokemon will appear in the game.  Battle & Get!  Pokemon Typing DS can be played either by typing on the touch screen or by using the wireless Bluetooth keyboard that comes packaged with the software.

Changes:  N/A

Japanese Release Date:  March 17th, 2012
American Release Date:  June 18th, 2012

Overview:  A crossover between Pokemon and the long-running Nobunaga's Ambition series of games!  Players and their pokemon encounter warriors, each based on a real world historical figure, on their quest to take over the seventeen castles of the Ranse region.

Changes:  N/A

Japanese Release Date:  June 23rd, 2012
American Release Date:  October 7th, 2012

Overview:  Two years after the events of 2010's Pocket Monsters Black and Pocket Monsters White, a new adventure begins!  Play as a new trainer as they travel through the Isshu region.  What's changed in the last two years?  What new Gym Leaders and facilities will there be to find?  And what of N and the Plasma-Dan?  

Changes:  N/A