I love my DS's enthusiasm about his special interests. We can tap into almost anything if we use his current interests. Here is a list of some of his interests over the years (he is 6 now):
trains
aeroplanes
elephants
satellites
spaceships
aerials
timezones
world cup 2010
flags
flight stats
Out of them all, aeroplanes has been the main theme. I know so much about them as a result