Mirror Clock
When I was 12 I took apart a clock and made it go backwards. I immediately realized this was awesome. It took me some time, however, to realize any use for such a feat, besides bragging rights. After a period of time I realized that, in combination with backwards numbers, this counter-clockwise clock would read correctly in a mirror.Instructions on how you, too, can do this are below. If you still aren't convinced, let me say that to successfully complete this task, you must reverse the polarity. The answer to every scifi engineering problem can now be utilized in the real world.
Here you can see the final result. I bought 2 of the cheapest clocks I could find ($6 from Fred Meyer if you hail from the Pacific Northwest - Target should do everywhere else). They are fairly easy to take apart, and if you fail and destroy it, it's only $6.
The first step is to take the front clear part off, and carefully pull off the second/minute/hour hands (they should just slide off with a little force).
Once the hands are off, the gear case in the back should be able to be pried out (a screwdriver might be needed to open up the latches holding it in place). The great thing about clocks is that basically EVERY (reasonably priced) CLOCK ON EARTH, uses this same cheap-o drive unit, so these instructions should apply to any clock you find.
After you have the gear case off, use your handy screwdriver or pocket knife to carefully pry off the round dial used to set the time.
Next, VERY CAREFULLY un-latch the back cover from the front cover. Here you can see the 7 or so small plastic gears that are contained within - some of which are held in place by the back cover. If you pry it apart violently (like I did) then small gears go flying everywhere and you have a nice puzzle on your hands. Not an insurmountable problem, but easily avoidable.
Carefully remove the only thing that is not gears - it's a small circuit board with a wind of copper wire. The circuit board lets off carefully timed bursts of energy from the battery, creating a momentary magnet out of the metal U piece via the wound copper wire.
When removing this piece, be careful of the small round piece that interfaces with the gear system.
After freeing this assembly, remove the metal U piece shown here. Guess what - it's has polarity! It's time to reverse the polarity! Take out the metal U piece, turn it upside down, and put it back in. That's it!
Now, whoever design this did a good job - the metal U piece + circuit board assembly can only be placed in the plastic case the correct way, due to the metal U piece not being symmetric. To ensure that the clocks they manufactured only went clockwise, a small hole in the metal U piece fit into a small plastic peg. I removed that peg so that the assembly could be placed back inside the plastic casing.
Now carefully replace the small round piece that interfaces with the gear system, snap the back cover in place, and replace the round dial that is used to set the time.
A quick battery test and you'll be able to see if you have a counter-clockwise clock! Here you can see my setup - to really drive the concept home I put my counter-clockwise clock next to a clockwise clock, and the whole thing next to my bathroom mirror. I'm geekin' out. Enjoy your counter-clockwise clock!
Here are the two images that I used such that my two clocks matched. If you are lazy and don't want to make your own, then just use these.