You can search your computer using Spotlight using search options like other search engines.
Not sure how long spotlight has been this way, but I found it very helpful when searching. You can enter a search query just like you would on Google, use a dash or minus in front of word(s) that you don't want to see in the results.
Example: apple store receipt -itunes kind:pdf
Would find all PDF documents that don't contain iTunes info and that were an Apple Store receipt that are on your computer.
Example: happy kind:mp3
Would find all MP3 files on your computer with the word happy in the file name or meta tags.
Example: happy kind:mp3 -"and you know it"
Finds all MP3 files on your computer like above but omits the kids song if "your happy and you know it clap your hands" while returning all other results like above.
[crarko adds: I tested this, and it works as described. There is an earlier hint describing other tips for customizing Spotlight searches using Terminal.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100525102059552