All the hints for geeky complicated UNIX searches aside, a nice little feature of the pre-Tiger launcher applications was the ability to search with shortcuts. For example, typing "MW" would locate Microsoft Word in a search, or "QT" for QuickTime. Well, this functionality can be achieved in Spotlight.
By placing your desired shortcuts into the Spotlight Comment field in the Get Info dialog box of any application (or folder, or document, or EXIF data in pictures... you get the point), Spotlight will locate these items!
[robg adds: While this will definitely work, you will have to spend some time adding your shortcuts to each application. Personally, I'm quite happy that Butler works in Tiger (I presume QuickSilver and LaunchBar do too, but I haven't tested them). I use Butler to launch stuff, and Spotlight (grudgingly) when I need to find something in the Finder. Spotlight is a pretty good search engine, but, the launchers are much better at launching programs and opening documents quickly.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050508195548611