Simon Memory Game Online

Here’s another memory game that’s fun to play, on the website for National Geographic (where I work). You get 10 seconds to memorize the position of nine images on a grid (you can choose numbers or letters instead). Some people find the numbers and letters easier to memorize than the images of landscapes or animals. You can adjust the difficulty of the game to make it easier or harder by adding or subtracting squares on the grid.
http://magma.nationalgeographic.com/ngm/2007-11/memory/memory-game.html