First off, love the show, highly entertaining and informative. Second, I have an idea for a build: modify a car stereo w/ built-in DVD player to become a portable, self contained, movie projector. I got the idea when I came across the Lumenlab projector kit which allows you to turn a normal AMLCD into an LCD projector. However, the largest drawback of this is the fact that this type of projector is HUGE. It is also a power hog with a metal halide lamp. To make this more "portable", my idea is to use a single DIN, dash-mounted car stereo w/ built-in DVD player and flip-up screen as a projection system. The added benifit of using the car stereo is that you get a multi-channel, high power audio amplifier for "free" with the DVD player. Here is an example of the type of stereo system I'm thinking about: http://r.ebay.com/6gZ2DL
The concept is simple, remove the existing backlight and cover glass to get to the AMLCD. Sandwhich the LCD between two Fresnel lenses. Place a high-brightness light source behind the LCD at the focal point of the first Fresnel lens. Place a projection lens triplet in front of the new glass stack and Voila! you have an LCD projector. Here is a brief tutorial on how to construct such a projector: http://www.engadget.com/2006/10/17/how-to-build-your-own-hd-projector-part-1/ Unfortunately, Lumenlab is no longer around so most of the links on that page don't work, but I did manage to find the afformentioned Lumenlab guide: http://www.scribd.com/doc/40526532/Lumenlab-DIY-Projector-Guide-v2-0 You can continue the engadget tutorial for more information as well.
As far as parts go, since we are using a much smaller screen, you don't have to find a gigantic Fresnel lens to build this. http://www.edmundoptics.com/optics/optical-lenses/fresnel-lenses/fresnel-lenses/2040 has smaller Fresnel lenses that I believe would work for this project. I'm not an optics expert but I would try and keep the focal lenght of the lens as short as possible to keep the projector as small as possible. Projector lenses are common and you can probably find a good deal on Ebay for one. Just make sure it matches the Fresnel lens picked. For the light source, a 400W metal halide lamp does not really work for me. I was thinking of a high-brightness "natual light" LED. Element14/Newark has several that will work http://www.newark.com/bridgelux/bxra-50c1600-b-00/es-rectangular-array-cool-white/dp/73T6212 The TPS40211EVM LED driver board would be an excellent driver for the bulb. It is also available from Element14 - http://www.newark.com/texas-instruments/tps40211evm-352/eval-board-tps40211-adj-700ma-non/dp/09R6648?Ntt=tps40211evm
What I envisioned is a self-contained projector w/ speakers that can be taken to movies in the park, church events, kids slumber parties, etc. The speakers could be built into the case/enclosure and would be driven by the car stereo speaker outputs. This will finally be a projector with decent sound 
. For power, a single 12V supply is all that is needed, although it needs to be capable of high currents for at least 2 hours (lenght of a typical movie). My estimate is a supply capable of 12V @ 18A (216W) will be required. You could use a 12Vbattery pack (22Ah rating minimum) or a car battery but those would be pretty heavy. You could also use an old ATX power supply if you knew that household mains was available.
I'm not sure this would work in just one show, but I think it would be a really neat project to see you tackle. My estimate for build cost is between $250 and $350 for materials but could be cheaper if you shopped for deals. I hope you will consider this project idea for an episode when you start scraping the bottom of the barrel for projects.
Again, love the show! Keep up the good work.
Regards,
Shawn Standfast