Infant-Stim Mobile

Really captures his attention for a long time.
There are different discs that they recommend you swap every once in a while, to keep their interest. They range from black and white, simple shapes to more complex, colourful ones.
My DS is particularly fond of the 'baby' shape!

I was dubious when my brother gave me this when my daughter was born, but she loved it pretty much from birth. The cards fascinated her from day one, and it was a similar story when my son was born.