Ever wondered how fun it would be to zap someone with a taser? Now you can. :D
If you follow the instructions you should be able to get a good shock out of this that not to lethal but I'm sure its not that hard to step this up from a good shock to a powerful weapon so be responsible with this and use common sense when choosing who to shock (don't go around shocking old people, small children or any one with a heart condition its just a bad idea).
Now that thats out of the way the taser we will be building sends out about one shock per second probable around 35,000-40,000+ volts at an estimated .01 milliamp (millionth of an amp) the shock is about enough to cause you to jump back a few feet if your not expecting it. Voltage and amperage are estimated since i don't have the equipment to accurately measure it.

P.S. sorry about the low quality pictures and bad lighting my good camera was KIA I'm working on getting a replacement camera to take better pictures

UPDATE: i got a new camera enjoy the high res pictures

Step 1: Parts List

most of the parts cam be found at radio shack or a hardware store
Electrical Portion
ignition coil 12v - you can get this from an old car at the junk yard for about $5. for this project you want to get one with only 2 leads. these come in all shapes and sizes so you may have to ask the people working there to help you. also try to save the mount you'll need it later but its ok if you cant
12v relay12v relay - radio shack should sell this
1000 u Farad capacitor1000 u Farad capacitor
1 u Farad capacitor1 u Farad capacitor
non conductive switch- i made the mistake of buying a metal switch and get shocked every now and then
wires- with descent insulation
electrical tape
wire capes
12v power source - i used 8 D-cells for this
soldering stuff

Mounting components
2 foot long, 1 inch thick, 2 inches wide board
6 inch long dowel 1 inch wide
small screws

Step 2: Wiring

now that you've got all the parts we start attaching 6 inch lead wires to all used the leads on the relay this will make your life simpler. connect all the wires as shown in the diagram when you finish connecting everything flip the switch to on and touch the line out and negative line out wire. if you did it right you should be very awake(AKA shocked).

UPDATE:3/11/08
right so i was going through and looking at this and i though I'd add a small section on whats happening here with the wiring just to clear things up.

1)The switch is flipped completing the circuit.
2)The the relay is closed and the 1 u farad capacitor and coil begin to charge while the 1000 u farad capacitor simultaneously charges
3)when the 1000 u farad capacitor becomes charged the relay breaks the connection and the coil and 1 u capacitor discharge shocking what ever may be touching the coils line out and the negative line out
4)the 1000 u capacitor discharges and the cycle repeats at step 2 through 4 until the switch is flipped

UPDATE:6/6/08
ok so imagine this is your panel on the back of the relay

- 1 - 2
- 3 - 4
- 5 - 6
| 7 | 8

these numbers should be printed on the relay however may be missing

when positive and negative are connected to 7 and 8 the relay should trip
when no current is running through 8 and 7 relay allows electric flow from {1 to 5} and {2 to 6}
when current is flowing through 7 and 8 the relay triggers switching the connection from {1 to 5} to {3 to 5} and {2 to 6} to {4 to 6}
if all this is true with your relay you have the same type of relay other wise you may need to rewire stuff

next 8 and 4 connect to the large capacitor on the negative side (side with NO indentation running around the rim.) 5 and 7 connect to the other side of the large capacitor.

1 connects to the positive side of the small capacitor and 6 connects to the negative side.

2 and 3 connect to nothing

other things to check look for shorts around the relay theres a lot of wires really close together

Notes
the different colors of the wires is simply to make it easer to differentiate the wires from one another
you might consider using a larger capacitor in place of the 1000 u farad capacitor since i noticed the coil isn't fully charged when it discharged so the resulting shock is like rubbing your socks on the carpet and touching something metal as opposed to sticking your finger in a wall socket.

Step 3: Mounting

by this point you have all the electrical components so your able to mount it how ever you like but this is how i did it. Mount your coil 4-6 inches from the front of the 2*4 using the mounts you salvaged from the car if you weren't able to salvage it use zip ties or duct tape. Next mount the 6 inch dowel 1-2 inches from the rear of the coil. for the batteries i mounted them on the bottom of the 2*4 but this does not work so well you can do it that way or try to come up with a better way to mount them. the switch was also a little tricky since mounting it to the dowel would be hard. for this step i mounted the switch to the side plate on an old pair of safety glasses then mounted that to the dowel. Finally you should have about a foot on 2*4 left this is there to counter the forward weight of the coil on mine I attached a string to help keep it level.

Notes
the batteries were falling out so i have since added a hinged section of plexiglass with a small latch

Step 4: All the Wires

finally you should have a bunch of loose wires hanging off use the electrical tape to help consolidate the wires so they don't snag on any thing then your done.
have fun zapping people.