Alfred[0] has to be one of the most valuable (as far as $/usefulness) pieces of software I've ever bought. Besides the Spotlight-style file/app search, can also manipulate files/dirs, does pasteboard history[1], and one-shot terminal commands; without having to drop whatever I'm doing for another window.
You can also use it for math expressions, type in URLs to quickly open them, search Google and Wikipedia. It's completely changed the way I compute. The only time I see the app tray anymore is when I accidentally make it spring up from the bottom with my mouse.
[0] http://www.alfredapp.com/
[1] not part of Alfred, but pbcopy/pbpaste in the terminal are your friends.