DisableTigerFeatures
I'veScott (sorry, Scott!) mentioned Spotless and I mentioned other methods for disabling Spotlight in the past, but today I discovered another program on the block that will help you turn off both Spotlight and Dashboard whenever you like: DisableTigerFeatures.
DisableTigerFeatures version 1.0.1 "can disable Spotlight and Dashboard, and if you ever feel like you need to re-enable them (or you are about to apply a Software Update), just press a button, and you're back to where you started." I think this is a useful feature that I wish Tiger itself included. In the meantime, you can use this program, but pay careful attention to the warnings: "Note: This application modifies IMPORTANT system files! Please be sure to have a backup before you attempt this!" Also, keep in mind that if you do disable Spotlight, then programs (like Mail.app) which use Spotlight for their internal search will no longer have search functionality.
To run, the program needs authentication from an Administrator and it gets this by launching the Terminal. For those of you who don't like the Terminal, consider yourself warned.
[via MacInTouch]