This was just a lark that had been itching in the back of my head for a while. It's a mains powered LED lightbulb.
Step 1: Supplies
There's not too many things you need for this project.
An incandescent light bulb.
A .47 microfarad 200V capacitor.
1/4 watt 1kilo ohm resistor
a pair of leds
and miscellaneous things.
Step 2: Assembly
You need to start by cleaning out the lightbulb, there are numerous instructables with this step and I will forgo it here.
The circuit consists of two LED's wired in opposition, I ground down the LED's just short of the die and glued them together to make a single double LED. Twist the legs of the LED's together, on one side solder the capacitor, the other the resistor. Simple.
Step 3: Test
Here I'm holding the circuit with a clothespin and sticking it into an outlet, this is of course, the recommended test procedure. ;-)
Step 4: The Bulb
Stick the circuit into the bulb and use some hot glue to hold it in place, be sure to have some cold water, you will burn you fingers. Try to center the LED in the bulb. Once you have the circuit in place, bend one of the leads over the base and secure it with aluminum tape. The second lead is twisted around a brass screw inserted into the hot glue. Check for shorts and you should be good to go.