I've just discovered a good one:

3yo DS was starting the throw a wobbly because I wouldn't let him watch any more TV. He had his fist raised and was looking for something to throw at me. I had a light-bulb moment:

"Do you want to use the vacuum cleaner?"

HELL yeah!

So now he is vacuuming the kitchen Going from past experience he eventually gets sick of the noise and effort... but I reckon I have one successfully distracted 3yo for the time being!