Water Powered Clock @ Jaycar Electronics $19.95
How much of a novelty is this. Its a water powered clock - if that wasnt already bleedingly obvious from the title.
I was originally just going to post this because of the novelty value but its having a look around its a good price as well. You can get a range of water powered clocks (I had no idea they even existed) with prices as low as $7 (Jaycar again) but I like this particular one with the two bottles either side.
The nearest other price was $24 for the same clock, although you may be able to find cheaper.