This was a quick project I put together to create portable/safe sparks. I got the general idea from Tesla Down Under's side but modified the design to fit the parts I had on hand.
I started out by gutting the charger out of a disposable camera, and removing the extra pieces (capacitor, flashtube, trigger coil, pcb etc). Then I reassembled it to make it as small as possible, and connected it to a 6uf/450v cap (2x 3uf/450v in parallel). Finally, I hooked it up to a 5 turn primary on a flyback transformer and used a 220v SIDAC to discharge the capacitor into the flyback when there is enough voltage.
Shrinking the charger circuit and adding the storage caps/SIDAC
I also added a 1 cell AA batter holder, then started to build it into a box I built out of some leftover hardwood flooring
Finished product which produces a spark about 1" long and makes a nice 'snap' about 1 shot/second when you press the big red button. The energy is low enough (probably a few tens of mJ at most) that is is fairly harmless, if somewhat painful to be shocked by. For more information check out its post on 4hv.org