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Behold, the Nichia NSPW515BS 5mm diffused white LED. All the other white LEDs I have seen are more suitable for flashlights than panel indicators. This LED is beautifully diffuse, with 70° dispersion and a milky translucent package. It is amazingly bright and works well with low current.
I discovered this LED at the LED Museum on their white LED page. Go pay them a visit, everything you ever wanted to know about LEDs can be found there, as well as info on the new purple and ultraviolet LEDs.
Getting back on track, the Nichia NSPW515BS 5mm diffused white LEDs can be ordered direct from Nichia, but the prices suck unless you are buying 100 or more.
Nichia High Brightness LEDs
NSPW515BS specs and order form
For small quantities, I recommend http://www.whitelightled.com/ who sells various white LEDs for $1.75 each plus $1 postage per order. I got 4 LEDs for $8 total using PayPal. It was quick, convenient, and the LEDs are fantastic. Note that the Nichia NSPW515BS 5mm diffused white LEDs are not listed on the website, but he sells them, you just have to ask.