I use OmniDazzle during my presentations to highlight clicks and other important information. OmniDazzle is a free program from The Omni Group—makers of fabulous software like OmniGraffle and OmniFocus—that lets you display special effects on your screen.
In addition to the spotlight effect that I use regularly, there are other effects such as a trail of pixie dust that follows the cursor or a bullseye that helps you find your cursor on the screen. After you launch the program, a simple keyboard shortcut (usually control + `) turns the effect on and off.
If you give demonstrations with your computer, try OmniDazzle to help your audience follow along.
Download OmniDazzle