Well, here's a fun 'n' simple project that can make big, fat, noisy sparks at least 2 inches long, and can be built very quickly and cheaply. It might be even more fun to use a marx generator than using a 'very complicated to build' tesla coil!
And to let you know, this "Quick & Dirty" Marx generator website helped me a lot to build this marx generator.
If you have no idea what is a marx generator, you might be saying this in your mind "What the hell is a marx generator!", read about it here on Wikipedia.
WARNING! This project generates very high pulse discharge voltages, which can seriously harm and could be potentially lethal to you and others that are careless to touch the output of the marx generator.
Step 1: So, how does it work?
The capacitors are charged up in parallel through the resistors, so they each become charged to the input voltage. When all of the spark gaps fires (sparks), the capacitors get effectively connected in series, therefor multiplying the input voltage by the number of capacitors and causing a long spark at the end of the marx generator.
Rb has a ballasting effect, it is used to prevent a continuous arc forming across the first gap - this prevents further firing of the marx generator. The value of the resistor will mainly depend on the type of power supply is used, in this case, we are going to use an 10M resistor for this marx generator on this instructable. However, you can reduce the Bb's value to try get more 'bangs per second' without causing an arc forming on the spark gap...
Now, you know how it works (I hope), so lets build it!