I'd like to recommend some games for the DS, if you want to list some for the PSP or GBA or N-Gage (god save you), please go ahead.

Lost in Blue:
This is a survival adventure game. The graphics are nice and the music is calming. You have to get off an island. While this game isn't a world rocker, it is very relaxing to play at night in the bed. A laid back game with good replay value. A nice change of gaming and nice use of the DS features, and they don't feel gimmicky as some jaded people would tell you.

Resident Evil:
A faithful port of the original. It's fun to have it portable, horrible voices and all. The rebirth mode is ok, but I found the original to be the best. The translation to DS is very good.

Metroid Prime Hunters:
Hands down the best FPS on the DS, and I don't think it will be losing that position anytime soon. Meaty single player mission, the boss battles get a little repetitive, but it retains the difficulty level started by the Prime series. Alot of backtracking and fast battles across several locales. This is handheld Prime, truly an excellent game, and the WiFi is very nice too, although as of this writing the match making service is screwy, but that will be sorted out.

There round one of my recommendations for the DS.

I'd definitely put in a vote for Trauma Center: Under The Knife.

I've had this game for only a few days now but it's maddeningly addictive, frustrating, challenging and has me completely engrossed already. You know the idea: you play a rookie doctor and through a story mode, you work your way through the ranks of the hospital and beyond, using the stylus to work on patients.

Firstly, the game makes a superb use of the DS' capabilities. The top screen shows all the dialogue and story mode sections, whilst the touch screen is used exclusively for operations and menus. With the stylus you use instruments such as lasers, bandages, scalpels, syringes, drains in a variety of combinations in order to cure increasingly difficult conditions.

What strikes me most about this game is how tense it is. Though the graphics aren't too clear (though with a weak constitution might have a problem with the awesome sucky/cutting noises though!) you've got the patients vital statistics constantly in flux, not to mention a time limit. The time limit ISN'T that constrictive as it is in most games - the majority of time is spent working on the patient and ensuring their vitals stay healthy. The operations usually last about 2 minutes and they come at you fairly quickly, interspersed with typical anime style story sequences.

What gives it a little more longevity is that any surgeries you complete in the story mode are automatically placed in the Challenge mode where you can attempt to beat your graded rank (A, B, C etc).

If you're looking for something a little different and you've had it with these do-nothing games and want your pulse raised a little, Trauma Center is definitely recommended.

I would love to recommend Phoenix Wright, Attorney at Law. This game is hard to find, now, but so much fun. In the game, you play Phoenix Wright, a lawyer, and you get to investigate cases as well as try them in the court of law. The game's anime stylings make it quite fun and over the top. "Objection!"
The technical stylings allow for a very good exploration of DS' capabilities. The top screen provides all the background, story, and character interaction graphics while the touch screen allows you to make your choices in what you'll do next, what questions to ask, and how you interact with the environment you are in (i.e. what to examine). This game is great fun, shows off the DS, and is very interactive. If you like crime dramas and don't mind that everything is not taken seriously, then this game is for you!!

I love pheonix wright and trauma center - there a quite a few games that are already hard to find for the DS and I've been collecting them... i bet when everyone realizes how awesome the system is they will shoot up in price. There are quite a few GBA games that are already worth $100+ new in packaging...

I also really like Trauma Center... Mario & Luigi: Partners in Time is also very good, as well as Advance Wars DS.