The clicking of keyboard keys is usually the result of the plastic of the keys hitting the plastic frame underneath. You could, in theory, put some sort of contact-preventing material there, but it would most likely lead to loss of precision and responsiveness. Better to get a spring-loaded keyboard with flat keys, such as the Logitech UltraX. No funky key placement, no extra gimmicks, but you will be sacrificing wireless. If you're keen on keeping your wireless, just browse your local selection for a laptop-style keyboard. They tap instead of clicking, but do try one out before buying. Typing out "The quick brown fox jumps over the lazy dog" should test all alphabet keys.
At least Logitech made non-clicking mice at one point, but users objected to not being able to tell when they had actually pressed the buttons, so the physical feedback was brought back. I'm guessing the clicking could be removed by removing the clicking parts, but it would most likely impair the buttons' ability to operate.
Edit: I was perhaps being too vague on the clicking. Those large, traditional keys are mounted in holes, and the fitting is usually loose. Thus even the slightest push will nudge the key around in its fitting, causing hard plastic surfaces to come into contact. Spring-loaded laptop keys are less prone to this, as the fitting and construction are better for quiet typing. A person's style of typing will account for some of the noise produced as well.
Case: FD Define Mini
Parts: P8Z77-M Pro µATX, MSI N650Ti-1GD5/OC, G.Skill 2x4/1600/CL9 DDR3U, Xonar DX, WD Red 3 TB, m4 128, RX-5300 PSU
Cooling: Noctua NH-U12P SE2 + Scythe SS PWM, 2x Noctua NF-P12
Extras: D-Link & Netgear powerline, Eaton UPS, Benq 24" TN, Ducky kb, Sensei Raw/R
idle & load: CPU 32 °C & 44 °C @ 300/600 & 600/800 RPM, GPU 35-65 °C @ 1200-1650 RPM
Last edited by Das_Saunamies on Wed Jun 27, 2007 3:05 am, edited 1 time in total.