This one is slightly less addicting that line rider, but still very cool. BallDroppings. A point on the screen drops balls. You use the mouse to draw lines to bounce the balls. WHen a ball hits a line, it makes a certain ping sound. As the situation gets really complicated, you get something that resembles modern music. Very very abstract modern music :P
Its pretty cool, but I dont know if you could play this for as long as line rider :P
Get it here