Knights in the Nightmare and its big sister from the GBA Yggdra Union.
GameStop gave me a fucked up copy of the artbook and its in bad shape now. the box is also bent and its so damn sticky from the damn shit they used to keep it stuck to the OST so even thats in bad shape. but still...

Rhythm Heaven

Final Fantasy IV

Mega Man Zero Collection

Castlevania: Dawn of Sorrow

World Ends With You

*soon to be* Golden Sun: Dark Dawn

Phantasy Star Zero.

I have a ton of DS games, but I have no clue which of them are valuable or not. I didn't know so many games had been discontinued.

Anyone know if they still make Pac-Pix or Devil Survivor?

I have Metroid Prime Hunters. I had to go to like 5 different places just to find it.

I also have the Game and Watch Collection

I think my most valuable DS game is Electroplankton. I actually found out about it in a National Geographic Kids magazine a long time ago. I decided to get it, but the only place I could get it was online. Then when it made it's appearance in Brawl, I assume the value of the game went up. Also, I looked on the game database, and very few other people have Electroplankton on VGC. I bought it for about 20 dollars, and now it's about 30 dollars

Tales of the Tempest

Tales of Inncoence

Osu! Tatakae! Ouendan!

Moero! Nekketsu Rhythm damashi Osu! Tatakae! Ouendan 2

Elite Beat Agents

Luminous Arc 2

Draglade

Custom Robo Arena (maybe?)

Naruto: Shinobi Retsuden (regretfully bought it days before the US announcement)

Yeah, that's about it. The Japanese-only ones are my most valuable but only because of that reason.