The red LED in these photos is a 1.7 volt 1100mcd and the white LED is a 3.6 volt 3000 mcd.
I bought both of these and the plastic mounting collars at Radio Shack.

I used an old 6 volt power supply that I had laying around for these photos.
You need to use a current limiting resistor to avoid burning out the LEDs.
Use the resistor calculator at the bottom of this page
The calculator script came from Bill Bowden's electronics page

Red button with LED mounted	White button with LED mounted
Red LED powered up	White LED has a slight bluish color
A view from the bottom showing the plastic panel mount	With the microswitch installed, you can still get at the leads for the LED
Red LED under a red button	White LED under a white button. I must have moved during this shot.
Red LED under a white button	White LED under a red button.
Red LED under a Player 1 button The horizonal Happs buttons have more room inside, and the plastic is a little thicker. This means you may want an even brighter LED for the horizontals	Red LED under a Player 1 button.
Here you can see both player buttons. Power is from the IPac You can barely see the glow because of the 150 watt flood light above my workbench	With the floodlight off you can see the glow much better