Google Importer is a Spotlight plug-in that can add a Google search to the list of results Spotlight returns. It is installed as a System Preferences pane with options to adjust how many results are gathered from Google, whether to show a link to an actual Google results page, and how many seconds to wait after the last key is typed to begin searching Google. Note: that last option only adjusts how long Spotlight waits to search Google, not the rest of your computer like many users have been asking for.
I haven't tinkered around with this, but it sounds like a nice idea as long as it doesn't hang the Spotlight search too much. Google Importer is donationware and available from Caffeinated Cocoa Software.