CR-2032 battery. LED Throwies. LED throwies consist of only a few inexpensive parts and can be made for ~$1.00 per Throwie. You can reference the parts list below or download the attached spreadsheet for more info on parts, part's numbers, vendors and application notes. Part: 10mm Diffused LED Vendor: HB Electronic Components Average cost: $0.20 avg per LED Notes: Cost reductions for larger quantities. Comes in red, blue, amber, white in both diffused and clear. Diffused works better than water clear for the Throwie application. HB has even created a Throwies packs page with deals on 10mm LEDs and lithium batteries! Part: CR2032 3V Lithium Batteries Vendor: CheapBatteries.com Cost: $0.25 per battery Notes: Cost reductions for larger quantities. Part: 1-inch wide Strapping Tape Vendor: Your local hardware store Cost: $2.00 for one roll Notes: One roll will make many throwies. Making Things Talk. Tutorials.
LED Throwies. Lithium Coin Size Batteries - CheapBatteries.Com. Toll Free: (877) VERY-CHEAP. LED Manufacturer - China. Disc Magnets. D125D (Showing Decimal Measurements) Auto On/Off LED Throwie. This is my version of the LED Throwie. The design isn't mine, this is just my mod of it. In the original design, the LED Throwie is on from the moment you put it together. This can be annoying if you're planning to make tons of these, or if you want to make them ahead of time but not have the battery run out. Someone has already posted a mod that adds an on/off tab to the throwie, however I've taken it one step further: in this design the throwie automatically turns on when it sticks to something, and turns off as soon as you remove it! It's just as simple to make as normal throwies, and doesn't require any extra materials either!
These also work great as simple LED pinch lights. Credit goes to everythingdigital for the idea (it was mentioned in a comment), but the implementation is mine. I'll point out that though this instructable may seem long or complicated at first, it's only because I wanted to make sure it was well documented. LED Throwies with On/Off Tab.