Tringo is a great game for waiting rooms and other places where you need a game you can easily pick up and put down.
Of course you can play it in a DS or DS Lite if you have one, but I leave it in my GBA SP, which tucks even more nicely into a corner of my purse, so I always have it available for waits. It's nice that the background changes between games, and the sound effects and music are well-done; they are not annoying like some games. It's hard to say a lot about such a simple game, but it's well worth the retail of $15, and even better if you can find it used or in the bargain bin. It's easy enough for anyone to pick up and play almost immediately.