Here's an easy electronics project for your favorite Dr. Who fan! Many of my helmet materials were found around the house or at Goodwill, so you can substitute in parts that are about the same size/shape.

I used:

Plastic army-style helmet. Goodwill carries these around Halloween.
Black spray paint
Silver spray paint
6" length of 3/4" PVC pipe
Cardboard. Scraps are fine, approx 2 square feet total.
Mason jar ring
Chopstick or pencil
Small dome-shaped object, approx 3" wide and 2" tall. A tennis ball cut in half would work.
Two plastic cups for the "ears" These should be semi-transparent to let your yellow lights shine through.
9v battery
9v battery cap attachment with wire connections
short length of light duty wire, approx 2 feet. Red and black are recommended.
2 yellow 5mm LEDs
1 blue 5mm LED
Electrical tape
Velcro tape. This is often sold in the garden section for attaching plants to trellises.
Craft foam, if you'd like to add padding to the helmet.
Super glue
Hot glue
Solder

Tools needed:

Drill with 1" keyhole bit and a very small bit for making LED wire holes
Scissors
Wire cutter/stripper
Hot glue gun
Soldering iron
Craft knife

Step 1: Building the Eyestalk

The eyestalk is a key feature of the evil Dalek! Moving from the outside towards the "head," the main parts are: the eye, the stalk support, and the connection to the helmet.

Eye:

Find your dome-shaped object. I used half of a spherical wood box I found at Goodwill, but you can use anything roughly the same shape.
Drill a hole through the top of the dome, making sure your PVC pipe fits snugly through the hole. My hole was about 1" across.
Spray paint the eye dome black, inside and out.
Cut a cardboard circle that fits inside your dome. Make a small hole in the center for the LED wiring to pass through. Spray paint this piece black.

Stalk:

Take your PVC pipe and drill a small hole straight through the pipe, about 1/2" from one end. Check that your chopstick (or pencil) fits snugly through this hole. This end of the PVC pipe will sit inside the helmet, and the chopstick will hold the pipe in place.
Break off a 3" piece of the chopstick, set aside.
Spray paint the PVC pipe silver. This will be the main support for your eyestalk.
Cut out circles from your cardboard scraps. I made six 3" diameter circles and two 4" diameter circles. Cut a hole in the center of each circle that's large enough to go around your PVC pipe.
Spray paint the cardboard circles black on both sides.

Connection:

Cut a cardboard circle that fits inside the mason jar ring, and cut a circle in the center that the PVC pipe will fit through.
Spray paint the cardboard silver.
Once it's dry, hot glue the cardboard into the metal mason jar ring.

Assembly:

Make sure all the parts are dry, so you don't smudge your paint.
Using lots of hot glue, slide the black circles onto the stalk and glue in place.
Glue the eye onto the end of the stalk without the hole drilled through it.

Step 2: Helmet and Eyestalk Attachment

Helmet Prep

Look at the front of your helmet and decide where you'd like the eyestalk to attach. Drill a hole through the helmet that's large enough to allow the PVC pipe to fit through snugly.
Hold the plastic cups up and decide where you'd like the "ears" to be. Cut the cups to fit, as needed. Drill a small hole in the helmet under the center of each cup, to allow the LED wiring to pass through.
Spray paint your helmet silver.

Attaching the Eyestalk

Slide the mason jar connection piece onto the end of the PVC, then slide the end of the pipe into the helmet. It should only stick through just past the hole you drilled, about 1/2 inch.
Push the short piece of chopstick through the hole in the PVC. Holding the stalk tightly against the helmet, add lots of hot glue to hold this assembly in place on the inside of the helmet.
On the outside of the helmet, make sure the mason jar connector is snugly against the helmet, hot glue the connector in place. The two connections should firmly sandwich the PVC pipe and hold it firmly to the helmet.

Step 3: Installing the LEDs

Now it's time to make your Dalek light up.

General wiring instructions:

It's really easy to wire these lights! Any time you want to make a connection, simply overlap the bare wire ends (remove a little insulation if needed,) hold the soldering iron tip on the wires to heat them up, then touch the hot wires with the end of your solder coil. It'll melt and seal the wires together. Wrap the connection neatly in electrical tape and you're good to go.
Try laying out all your connections and testing them with a battery first. Make sure you're creating a big loop, always connecting positive to negative.

Eye light:

Find the black circle that fits inside the eye dome. Thread the blue LED through the center hole.
Cut short lengths of the red and black wires. They need to be long enough to run through the eyestalk and up to the crown of the helmet, where the battery will rest. Give yourself a little extra to work with!
Wire the positive (slightly longer) end of the LED to the red wire. Secure the connection with electrical tape, then wire the negative side to the black wire.
Thread the wires down through the eyestalk and into the helmet.

Ear lights:

Thread the yellow LEDs through the helmet holes. Flexing the wires flat against the helmet should keep the light in place, but you can tape it down if needed.
Grab the red wire (positive) coming from the earstalk and attach it to the shorter wire (negative) of one yellow LED. Take the black wire (negative) from the earstalk and attach it to the longer wire (positive) on the other yellow LED.
Finish your wiring by attaching the battery clip in the same manner.If you aren't sure which end to attach where, it's fine to connect the battery and touch the wire ends together to make sure your circuit is working.

Battery:

Attach the battery clip to the battery, and your LEDs should light up.
Hot glue a short piece of velcro tape into the crown of the helmet, creating a batter holder. I used a few pieces to keep the battery from shifting as I walked.

Step 4: Finishing Touches

Add foam to the inside of the helmet to ensure it sits firmly on your head.
Once you're sure the LEDs are working, glue the plastic cups onto the helmet to create the "ears." It was difficult to photograph, but mine had a nice yellow glow at night.

Your Dalek helmet is complete! Exterminate!