Hahah seriously so many game suggestion topics. Geez! 😛 But umm...well i'd definitely say Mario Kart DS. I know I loved it when I had my DS. Sonic Rush was really good as well. But really...Mario Kart DS is all you need for a while.

lol...

Elite Beat Agents... For a game entirely built around mostly 'meh' music by 'meh' artists, it kicks some pretty big arse...

The Ace Attorney series. If you only get one, you have to start with the first. The lackluster, one path only game play can't even scratch the amazing story telling. So much time went into the translation... and there are so many pop culture jokes.

Mario Kart and Tetris are also decent choices. If you are in to old school RPGs, Final Fantasy 3 is good (with IV to join it soon). Pokemon is decent too, if you are into that sort of thing.

Advance Wars: Dual Strike
That is probably the greatest game you can possibly buy for the DS. Almost endless replay value. But I don't know if you like turn based strats.

Definitely get Mario Kart DS. Wi-Fi is pretty entertaining for a bit, and it might take a while to get all the racers and karts, so there would be some good time spent with it.

I really liked Kirby Canvas Curse only due to how well the touch screen is used. I think it'll only last a long time if you are a completist, as the main levels are easy to beat, but it takes a while to collect the 300 medals.

Pokmon Diamond and Pearl are pretty good if you like some pokeymans.

And finally, Meteos. Again, I think you'll get the most out of this game if you are a completist, as it's pretty hard to get all the planets and stuff like that. It's also a good game to have just so you can play a round every now and then.

I got Hotel Dusk for free when I bought my DS and had an awesome time with it, but it might not be everyone's cup of tea.

Cooking Mama is addictively fun too.

Trauma Centre. I can NOT stress this one enough. It is incredible, in ever sense of the word. The only DS game that has made me swaet and given me hand-cramps.

Ace Attorney. If you do not buy it then I can never love you again, Spiner.

Since Mario Kart DS and the Ace Attorney series have already been stressed, I also recommend Star Fox Command. Once you get the hang of it, it's one of the ultimate DS time-killer games, next to Mario Kart DS, of course. If it's also your style, Legend of Zelda: Phantom Hourglass is a solid addition to a DS library.

In no particular order, I recommend...

Super Mario 64 DS
Sonic Rush
Mario Kart DS (I've lost mine! )
Final Fantasy III
Star Fox DS (short, though)
LoZ: The Phantom Hourglass (Though I haven't beaten it)
Pokemon Diamond/Pearl

~Nytloc Penumbral Lightkeeper

Naturally, Dawn is also implied... but moreso this.

Dawn of Sorrow was better than Portrait of Ruin. Portrait of Ruin added barely anything new other than using two characters, which is cool but turns out to be completely unnecessary; I played through the entire game using only Jonathan, and barely used Charlotte just because you have to use her shapeshifting stuff sometimes.

Thanks for the suggestions, guys. I'll put them under consideration.

Jump Super Stars and Jump Ultimate Stars. Think like a cross between Super Smash Brothers and Shonen Jump. You unlock characters from various series (Jump Ultimate has Vaizard Ichigo and Afro Luffy, for example). It's insanely fun.