Following the DIY sensor bar initially created by Doctabu, I created one of my own.
My requirements was that I move the Wii around and needed flexibility on the actual play distance. To do that, I wanted two IR LEDs that could be easily repositioned. Thus, a quick trip to the local electronics store yielded me 2 infrared LEDs, 2 battery holders and 2 resistors and 8 AA batteries.
I was aiming for brightness in the IR spectrum and some research had shown that LEDs with a lower 850nm wavelength produced higher degrees of brightness than the higher wavelengths. In the end, my electronics store had a limited selection anyway. The LEDs I was able to obtain were 1.7 forward voltage with a peak current of 50mA. I had a 4 x AA battery pack so that required a 100ohm resistor for each. If you have any other type of LED, your resistor requirement would change. For example, if you choose to use a 2 x AA battery pack for this LED, you'd need a 56 ohm resistor.
Once complete use a digital camera to see the IR light and check that your connections work.
I've attached a spreadsheet to calculate the right width that the LEDs need to be spaced apart for any given play distance.