In the Spotlight menu's search box, you can control-click a word and use the contextual menu to spell check your search term, or run a Google search with that term, etc.

[robg adds: This may be obvious to others, but I'd never thought to try control-clicking in the Spotlight search box. I'm not sure I'll ever use the feature, but now at least I know it's possible. Obviously, this hint is for 10.4 and 10.5 only, but I don't have a category for "10.4 or newer." As such, I chose to leave it uncoded, given that the vast majority of users here are on at least 10.4. That's how I'll probably treat all such hints going forward, too, unless someone has a better suggestion.]