For Maker Faire 2011 our family built a Samus costume for my brother. It has over 100 arduino-controlled LEDs and sound effects.
I'll just walk through the individual components and say a little about each.
The cannon was made out of a piece of 3 inch (inner-diameter) schedule 40 PVC which we glued EVA (ethylene-vinyl acetate) foam to, covered in a craft sealant (called "Mod Podge Glue"), then painted. The front muzzle piece is just a 3-2.5 inch PVC adaptor with a piece of orange transparent acrylic glued inside. Behind the acrylic are two sets of LEDs, 6 yellow and 6 red, which are independently controlled by an arduino in the backpack.
Near the back of the cannon, there are two styrofoam* protrusions on opposite sides of the barrel. One houses a control panel that has buttons where you can 'unlock' the cannon by typing in a certain combination (once you unlock the cannon, you can shoot by pressing a button inside the PVC tube). The other has a speaker imbedded in it, which plays cool sounds from the game Metroid when you push buttons and 'unlock' the cannon with the right combination. Both of these are controlled by the arduino stored in the backpack (you can see the cables running from the cannon to the backpack in the main photo above).
Pressing a button inside the PVC tube plays a sound effect and flashes the LEDs in the barrel. If you hold the button down, and then release, it plays a 'charge up' sound effect and then a shooting sound effect.
I made the backpack out of vacuum formed plastic and some scrap PVC. The master mold for the vacuum forming was made out of styrofoam* covered with bondo. The backpack held all the electronics for the whole suit. We had a 9V drill battery in one "turbine" and the arduino and sound shield (which we used to power the speaker) were stored in the other "turbine".
The Chest Plate
The chest plate was also vacuum formed plastic. We also imbedded some LEDs by gluing them into transparent green acrylic, then gluing the acrylic behind the cut-outs we made in the chest plate.
Making the shoulder balls taught us how to mold and cast with silicon and urethane resin. First we made a master mold with a large styrofoam sphere, foam core, plaster of paris, and bondo. Them we made a negative out of silicon, then cast the final pieces out of urethane resin. We also imbedded LEDs in the 'groves' just by drilling holes and gluing the LEDs in from the back.
We walked into a motocross supply sore and said "we want the cheapest motorcycle helmet you've got". They looked at us a little strange, but we explained that it was just for a costume, and one of them was actually really into Metroid and thought it was awesome that we were making a samus suit.
All three protrusions on the helmet are styrofoam* covered in bondo (the two 'muffs' near the ears on each side, and the 'ventilator' near the mouth). The tubing connecting these components is just electrical conduit. Aside from stenciling the correct visor shape onto the wind-screen and putting a little translucent green plastic behind the visor, that was about all we did for the helmet.
The rest of the body armor was either vacuum formed plastic, or just thin, painted, EVA foam which velcro-ed onto the black jumpsuit he was wearing underneath.
I made the molds for the vacuum formed pieces out of styrofoam* and this cool epoxy resin stuff called Magic Smooth that you can prepare in large qualities and then smooth onto your work with water until its really... smooth. Anyone whose worked with bondo knows that getting anything smooth or even requires a ton of standing. This resin stuff was great though because there was barely any sanding involved after it dried.
Once again, we imbedded LEDs into the vacuum formed pieces by gluing them into green acrylic, and then gluing those under the plastic.
* The pink 'styrofoam' we used was technically called EPS (extruded poly-styrene) which is very similar to styrofoam, but technically not the same. However, we did use actual styrofoam for the shoulder-balls.
Notes on Vacuum Forming:
We used 1/16" polystyrene plastic for all of our vacuum-formed pieces. Its really easy stuff to use, and pretty easy to find (we got all of ours at Tap Plastics). You cut out a section of the plastic, clamp it in a frame, stick it in the oven at around 225 F for 10 minutes, then press it over your master mold on the vacuum forming table.
Building the table itself is probably the most complicated part. We sort of just winged it with the design. Ours is just a 2x2 foot square box made out of MDF, peg-board, and some scrap 1x4 inch pine we had lying around. There are holes for vacuum cleaners on either side of the box. The idea is: when you turn the vacuum(s) on and press the oven-softened plastic over your mold, you complete the seal around the edges of the peg-board with the frame thats holding the plastic. Then, each hole in the peg board turns into a mini-vacuum cleaner, and the plastic gets sucked to the table. All air pockets between the plastic and your mold get sucked out. After several seconds, the plastic cools again and hardens, and you are left with a 'shell' of your master mold.
That being said, there are several things to consider when you make your vacuum forming table. Make sure that you calk the inside seems of the box before you completely assemble it, and when you screw the last 'face' of the box on, make sure to calk the joints so the box is air tight (aside from the holes in the peg-board). Also, depending on the strength of your vacuum cleaner, you may want to add 2 vacuum ports in your table instead of just one, you'll get stronger suction this way. Also since there is considerable pressure on the top and bottom of the table during the actual forming process, if you want to make a huge table (bigger than 2 by 2 feet), you may want to add supports periodically throughout the inside of the box so the top doesn't collapse when you are forming.