Two come to mind.
For admiration, removing a stuck thermostat on the 350 in my K-5 Blazer, finding a discarded orange juice carton in the parking lot and making a functional gasket out of it. It worked for a couple of days until I got a chance to replace the thermostat.
For just don't give a damn, the actuating rod for the ignition switch on my F-150 had worn out. After a week or so of having to pop the hood and use jumper cables between the battery and the ignition solenoid, I spent the $5 and added a starter button.

My old '87 Crown Vic wagon battery started mysteriously dying. It was, to say the least, annoying. I was trying to figure out what the h was going on when one morning on the way to work I noticed the light for the rear window defroster flickering on and off. Ah ha!
There was a three position momentary switch for it (see below for an example not from my car).
<img src="http://zachbardon.com/tour/wp-content/uploads/otherdash.jpg"&gt;
The defrost switch is on the right of the HVAC control head. I had two potential causes: the switch was going bad or my car was possessed. I called the local Catholic church to see how much an exorcism cost. They aren't cheap. Apparently they had some unexpected costs come up. So, I decided to try fixing the switch to see if maybe that was it. I stuck a nickel in the switch slot to hold it in the OFF position. That worked.

On one particularly abusive moto weekend we repaired a pickup's cracked exhaust manifold with high-temp silicone, baling wire and a metal tennis ball can. The fix lasted about 160 miles, or two miles short of home.
A HiLux 4×4 was another casualty – a run through a narrow washout resulted in wicked positive camber to the front wheels and additional abuse trashed the rear u-joint. We found a local farmer to weld some rebar to the straightened links up front and dropped the rear drive shaft, resulting in a front-wheel drive HiLux. The owner drove with those "temporary" fixes in place for the better part of 6 months.
I've never seen a leather belt used in place of a fan belt, but I have a buddy (a Ferrari mechanic, of all things) who used a pair of ladies' nylon stockings in that capacity. I never asked him where he got them.

My F100 has had a plywood tailgate for years. I've never been able to find a replacement in a junkyard, and I'm too damn cheap to buy a new one from a catalog. At one point I spray painted "Pro Net" on it, but that faded out. Nobody gets the joke anymore, so the hell with it. Also, at one point somebody gave me a Honda CB350 twin that an old girlfriend had abandoned in his yard when she split. I got it running, and covered the torn up seat with duct tape. I rode the thing around town for quite a few years, and just kept replacing the duct tape. By the time the poor thing finally died, the seat must have had about fifteen layers of tape under the most recent application.

Yeah, I did the string through the window for the broken throttle cable on my Volvo 240, and rolling up the window is cruise control! But my shining moment is the fifth of July, on the grapevine. I t's 99°, and I blow the upper radiator hose on a '76 Chevy van. It didn't take long to realize that even with water refill and duct tape, I had twelve miles to the top, I was only going to make a 1/2 mile at a time, with 30 min cooldowns, and the fam was melting in the back. Then, I remembered I had safety wire and twisters in the back. I applied about seven layers of duct tape, and then put about eight loops of safety wire on (it was one of those convoluted, universal water hoses). We made it to the top, and I stopped at the bottom and it was still holding. It held all the way home and I forgot about it. I sold the van three years later and the buyer asked what was with the hose, I told him it might need replacement.

When all you've got are bicycle parts and tools, everything starts to look like a bicycle.
One day, the idle speed set screw from my 1989 Peugeot 405 S disappeared, and the car would run, but not idle. Lacking the correct part, I used a chrome-plated steel Campagnolo crank arm bolt threaded into a plastic Schrader inner tube valve cap to arrive at an OD slightly larger than the original set screw's. I then had someone start and run the motor, while I tapped the unit into the open hole enough first achieve a tight seal and then set an idle speed approaching normal. Good to go!
I always liked to think that until VW introduced the Phaeton, with its outsourced to Vicenza trunk hinges, that I had the newest Campy-equipped automobile on the road after they stopped making wheels.

Fixed the cruise control in my 1986 300zx Turbo with a dime!
Cruis control wasn't working, found that the culprit was a missing pad on the clutch pedal. Therefore the switch that disables the cruise when you press on the clutch was never activated and the car always thought I had my foot on the clutch. It is a stupid design if you ask my and the rubber bumper is like a $30 part. I found a dime on the floor of the car and used electrical tape to hold in place.
Still works to this day!

Got to disagree there, facelvega. I looked on the Merriam-Webster website and they say Jerry rig is correct

The worst I've seen in the field is… this. Might finally submit it to "There, I Fixed It."
<img src="http://img.photobucket.com/albums/v648/smokyburnout/08-22-09_1756.jpg&quot; width="600">
<img src="http://img.photobucket.com/albums/v648/smokyburnout/08-22-09_1822.jpg&quot; width="600"/>

I've heard it put another way, but it's a more common slur so I won't repeat it, just offhandedly mention it.

I'd probably know that if my ID account wasn't created with an email address that is basically inactive. I never check it.

Most Field Expedient:
The clutch went out on my Willys when I was driving home from work. Pedal went straight to the floor and stayed there. I drove for a couple of block with no clutch, and while it turned out I could start from a dead stop in 1st using only the starter, I decided that might be a bad idea. I pulled over and climbed underneath to take a look. Fortunately a '54 Willys has a mechanical clutch. Unfortunately the idiot I got it from had assembled the linkage with bolts and non-lock nuts, instead of the clevis and cotter pins with which it was designed. The only things that I had were some bits of old 12ga cloth wrapped wire left from when I tore out the stock wiring harness. I managed to lash the linkage back together with it, and it held for the 2 miles home through heavy traffic.
Most Elegant:
The ICV controller in my '84 325e burnt out. After the resulting constant idle bounce between 400 and 2000rpm got me into 3 unintentional stoplight races (all of which I lost for failing to know were happening) I decided I should fix it. The actual part would have cost almost $300 from a junkyard, and far more from the dealer, so that wasn't and option. I had read about a fix where you just drill a correctly sized hole in a penny, and wedge it into the air line as a form of control, but that sounded a bit crude. What I ended up doing was using a brass gate valve (from a garden hose) and some barbed fittings to replace the original electronic ICV with a new, much shinier, manual one. It worked like a charm and a couple of times a year, as the air temperature and humidity changed, I would just readjust it to keep my idle nice and smooth.

I hit a erosion control "water bar" at speed on a remote fire road and bottomed out so hard that I sheared off the drain plug on my broncos fuel tank. after stopping I dove underneath and stuck my palm over the hole to stop the gusher of gas pouring out. My passenger grabbed the only thing we had to catch the fuel, my ice chest, and dumped all our weekends ice, food and drinks on the floor and slid it under the rig to me. We caught the remaining five gallons out of what was a full tank. We decided to head home and made it back about 90 miles to Seattle with the ice chest ratchet strapped on the passengers side of the hood with the fuel line shoved into the drain valve thingy gravity feeding the carb. The best part was stopping for gas on the way home and topping off the cooler. I still use the ice chest although it had to sit out in the sun all summer for the smell to leave the plastic.

I was driving a new 1980 Chevy 3/4 ton truck with about 2500 miles on it. I was towing an 8 horse trailer, fully loaded with racehorses and equipment. As I passed an irrigation trailer on the highway, some drops of fluid landed on the windshield. That didn't seem unusual, except that the cruise control cut off at the same moment.
The same sequence occurred about three more times (minus the farm equipment), so I took the next exit and stopped to lift the hood. The fluid was from the transmission. The positive battery cable had been rubbing on the transmission cooler line, worn through the insulation and shorted out on the cooler line. While shorting out it had burnt a hole in the cooler line (the fluid on the windshield). Every time it shorted out the electrical system it would cut off the cruise control.
I wrapped the metal line for the trans cooler with multiple layers of electrical tape. I then slit a piece of fuel hose lengthwise to fit over the tape, then wrapped it in more tape. Finally, I used four evenly spaced hose clamps on the outside of the tape.
I taped up the battery cable, looped it up where it wouldn't rub and topped off the transmission. We watered the horses and got back on the highway; total of 30 minutes. When I turned the truck over to the other trainer, I warned him to have it repaired ASAP. He drove it most of the summer and never had to add fluid.