My collection:

Pokemon Pearl
Pokemon HeartGold
Kirby Super Star Ultra
The Legendary Starfy
Sonic Rush
Sonic Rush Adventure
Mario Kart DS
Kingdom Hearts 358/2 Days
New Super Mario Bros.
Mega Man ZX
Mega Man ZX Advent

That's it for my collection ,tell yours! I'll be glad to hear it.

Pokemon Platinum
Pokemon HeartGold
Pokemon Mystery Dungeon: Explorers of Sky
Drawn to Life
My Sims
Phoenix Wright Ace Attorney: Trials and Tribulations (Epic win :3)
Mystery Dungeon (Not Pokemon, but made by Chun Soft)

My sister has better games than me, like Professor Layton, so I play her games a lot also. I just sold Madden 08 and MLB 2K7 as well.

Pokemon Heartgold
Pokemon Diamond
Pokemon Mystery Dungeon Explorers of the sky
Super Mario DS
Mario Kart DS
Kirby Super star Ultra
Yoshi touch and go
Henry Hatsworth

The following are games My Brother owns but shares with me.
Legend of Zelda Phantom Hourglass
Legend of Zelda Spirit Tracks
Pokemon Soulsilver
Pokemon Platinum
Scribblenaughts
Mario and Luigi Bowsers Inside story
Advance Wars Days of Ruin
Ace Attorney Miles Edgeworth
Ace Attorney Justice for all
Ace Attorney Trials and Tribulation

So many. O.O

Legend of Zelda Phantom Hourglass (Can't find it)
Pokemon Diamond
Pokemon Platinum
Mario and Luigi Bowsers inside story
Pokemon Hear Gold

Gosh you guys are going to kill my fingers 'cause my list is long.
I have:
Heartgold
Platinum
Diamond
Mario and Luigi: Bowser's inside story
Mystery dungeon: Blue
Mystery dungeon: Explorers of time
Mystery dungeon: Explorers of sky
Pokémon Ranger
Pokémon Ranger: Shadows of Almia
Fossil fighters
Scribblenauts
Spectrobes
Spectrobes: Beyond the portals
Spore creatures
Drawn to life
New super Mario bros. DS
Cloudy with a chance of meatballs
Tank beat
Cars: Mater-nationals
Brain age 2
Nintendogs: Lab and friends
Legend of Zelda: Phantom hourglass

Some of these games were presents meaning I didn't choose to get them.

Heartgold
Platinum
Final Fantasy III DS
HAD Phantom hourglass...and pearl.
Lost explorers of time
Mystery Dungeon Blue Rescue Team

Not much here.

I have enough:
1. Mystery Dungeon Blue
2. Mystery Dungeon Explorers of Time
3. Pokémon Diamond
4. Pokémon Pearl
5. Pokémon Platinum
6. SimCity
7. SimCity Creator
8. Bomberman
9. Mario Kart DS
10. Super Mario 64 DS
11. Mario Party DS
12. New Super Mario Bros
13. Super Princess Peach
14. Mario and Luigi Partners in Time
15. Mario and Luigi 3 (Bowser)
16. Pokémon HeartGold
17. Themepark (cheap $10 game from Target)
18. Animal Crossing
19. Nintendo DSLite Browser (though I can't use it anymore)
20. Professor Layton Elisian Box
Edit: 21. Yoshi's Story

I believe I'm missing 1 or 2, though that is about everything.

Mario and Luigi: Bowser's Inside Story
Mario and Luigi: Partners in Time
Mario Kart DS
Mario Party DS
New Super Mario Brothers
Picross DS
Pokémon Diamond
Pokémon HeartGold
Pokémon Mystery Dungeon: Blue Rescue Team
Super Mario 64 DS
Tetris DS
WarioWare Touched

And my sister has Brain Age, Nintendogs: Chihuahua, and some Brain Age clone.

I also have the Datel Games 'n Music card. It is basically like a flash cart, but it only plays homebrew and not actual DS ROMs.

Metroid Prime: Hunters- First Hunt
Super Mario 64 DS
Trace Memory
Guitar Hero: On Tour
Pokemon Platinum
Pokemon Mystery Dungeon: Blue
Pokemon Mystery Dungeon: Explorers of Time
Pokemon HeartGold
Pokemon SoulSilver
Sonic Rush
Sonic Rush: Adventure
Kirby Squeak Squad
Animal Crossing: Wild World
Transformers: Autobots Version
Metroid Prime: Hunters
Rhythm Heaven
Yoshi's Island DS
Mario and Luigi: Partners in Time
Mario and Luigi: Bowser's Inside Story
Call of Duty: Modern Warfare Mobilized
Final Fantasy III
Mario Kart DS
New Super Mario Bros.
Phantasy Star 0
The Legend of Zelda: Spirit Tracks
Fire Emblem: Shadow Dragon

... Duuuuude, that's a lot.

EDIT: Forgot DSiWare!

WarioWare: Snapped!
Art Style: AQUIA
Brain Age Express: Arts and Letters
Brain Age Express: Math
Flipnote Studio (two copies on each DSi)

Am I the only one who has 2 DS games only?

Pokémon Platinum
Pokémon SoulSilver

This is going to destroy my fingers...

Brain Age 2
Flash Focus
Drawn to Life
Kirby Super Star Ultra
TLoZ Phantom Hourglass
TLoZ Spirit Tracks
Pokemon Diamond
Pokemon Pearl
Pokemon Platinum (lost )
Pokemon Heartgold
Pokemon Soulsilver
Pokemon Ranger (also lost )
PMD Blue Rescue Team
PMD Explorers of Time
Pokemon Ranger: Shadows of Almia(Lostified )
PMD Explorers of Sky
Spore Creatures
New Super Mario Bros.
Mario Kart DS

I'm sure that I forgot a few...

Pokémon SoulSilver
Pokémon Platinum
The Legend of Zelda: Spirit Tracks
Mario and Luigi: Bowser's Inside Story
Kingdom Hearts 358/2 Days
Rhythm Heaven
New Super Mario Bros.
Chrono Trigger
Pac-Pix
Sprung(a horrible game I thought I was cool to get cause it was T-rated a LONG time ago xD)
Feel the Magic XY/XX
Final Fantasy III
Drawn to Life
Mario Kart DS
Kirby Superstar Ultra
The Legend of Zelda: Phantom Hourglass
Elite Beat Agents
Kirby Squeak Squad

I have-
Pokémon SoulSilver.
Pokémon Pearl.
Pokémon Platinum.
Pokémon Dash.
Pokémon MD Darkness/Time and Sky.
Mario and Luigi: Partners in Time.
Mario and Luigi:Bowser's Inside Story.
WarioWare Do It Yourself.

currently? *ahem*
Pokemon Diamond
Pokemon Pearl
Pokemon Platinum
Pokemon Soulsilver
Pokemon Troezi
Pokemon Myster Dungeon: Blue Rescue Team
Pokemon Mystery Dungeon: Explorers of Time
Mario Kart
Kirby Squeak Squad
Kirby Super Star Ultra
Wario Master of Disguise
Phoenix Wright Ace Attorney
Phoenix Wright Ace Attorney: Justice For All
Phoenix Wright Ace Attorney: Trials and Tribulations
Professor Layton and The Curious Village
Professor Layton and the Diabolical Box
Scribblenauts

Actual Games:
- Pokemon Black
- Pokemon HeartGold
- Pokemon Platinum
- Pokemon Diamond
- Pokemon Pearl
- Tetris DS
- New Super Mario Bros.
- Final Fantasy IV
- Nintendogs: Chihuahua and Friends
- The Legend of Zelda: Phantom Hourglass
- The Legend of Zelda: Spirit Tracks
- Kingdom Hearts: 358/2 Days
- Atari Greatest Hits Volume 1
- Metroid Prime Hunters
- Super Mario 64 DS
- Mario Kart DS
- Spectrobes: Beyond the Portals
- Sonic Rush
- Mario & Luigi: Partners in Time
- Guitar Hero On Tour

Other DS Programs:
- Korg DS-10
- Nintendo DS Browser

And now, my fingers are killing me... XD

My DS Game Collection, sorry for the bump:

- Burnout: Legends
- Sonic Rush
- Sonic Rush Adventure
- Sonic Colours
- Sonic and Sega: All Stars Racing
- Pokemon Pearl
- Pokemon Platinum
- Pokemon Soulsilver
- Pokemon Black
- Pokemon Mystery Dungeon: Blue Rescue Team
- The Legend of Zelda: Spirit Tracks
- Megaman Zero Collection (WE NEED ZERO 5!)
- KORG DS - 10 Plus Synthesizer

Pokémon Diamond
Pokémon Mystery Dungeon Explorers of Time
Pokémon Ranger Shadows of Almia
Pokémon Platinum
Pokémon HeartGold
Pokémon White
Pokémon Ranger Guardian Signs