For us, there are a few select games that never leave the immediate vicinity of our DS. Tetris DS and Space Invaders Extreme can be immediate sources of instant bliss, so we're never without them when out and about in the real world, where the danger of not being able to game can be very real and present. What about you all?
What are those few games that get constant rotation in the cartridge slot of your DS? What game (or games) do you constantly come back to for amusement?