Also be aware that if you are looking for a lot of brightness, some of those LED's might not do it for you. As a point of reference, the lights in the NovaGems we sell are about 5x the brightness of the standard "superbright" LED's. The really high MCD rated "superbrights" usually have very narrow view cones, which isn't what you will want for your buttons.
When selecting LED's, look for "luminous flux", which is calculated based upon view angle and MCD. Some lower MCD LED's put out just as much light, just at wider angles.
Also, a quick note on the GGG diffusers. The product has just been updated with new material that works incredibly well, is thin and very durable. And because they are now quicker to manufacture, the price has been lowered as well.
RandyT