Flashing and/or color cycling LEDs are
obnoxious. Don't do it. I have one of
these on one of the fans in my case, and it makes the inside of my PC look like a disco. It is distracting.
Much cooler is the ThermalTake
CoolMod which I have on another fan. It glows a nice blue whenever the PC is on, and it flashes red when the IDE hard-drive is busy. (I wired the case hard-drive LED to my SCSI host adapter.) So, you get the cool color change and blinking lights when the PC is busy, but when it is just sitting there with no disk activity, the colors do not blink or cycle.