LEDs of all types: Individual LEDs to 12 Volt DC tail lights white or colored. Example (Oct 06): Search for "led white mcd 100" and one of the sites you get is "100 PCS Mega Bright White LED 10mm 130,000 mcd" for buy it now price: $15.99 with shipping at $15.00. I have watched the mcd rating go up year by year. It was around 10,000 mcd in 2003. The longer you wait the higher it goes. Another example: Search for "led yellow mcd 100" and one of the sites you get is "100 PCS Mega Bright Yellow LED 10mm 60,000 mcd" for buy it now price: $9.99 with shipping at $16.00. Searching for "LED Bulb" will give a result that one can look for the 12 volt versions.
Dip Compass can sometimes be found by searching for "dip needle" (used for determining earth's latitude and for finding iron deposits)
High amperage 3 phase Diode Bridge Rectifiers are quite useful in converting AC to DC to charge battery banks. Can be used with generators, hydro plants, and wind power. Search for "diode bridge". 3 phase are more versatile in that they can also be used with single phase AC. A pre-made bridge is also better than trying to put this together from the individual diodes. A typical current price is $54.95 with shipping of $9.55 for 800 Volt 150 Amp. Get the highest amperage you can afford.
DC permanent magnet motors that can be used as DC generators.
Rebuilt car alternators that can be used to make for hydro power that charges 12 Volt batteries.
DC charging controllers that dump load when voltage is higher than a given value can be found on this site.
Hearing Aids sound amplifiers (behind the ear) battery operated around $10.00
Offered by Mike.