This list misses "Everything", the instant file search engine. It's the app I miss the most on Linux and OS X. (http://www.voidtools.com/)

Everything's secret is that it taps into the file system journal to instantly know about any file name change. On *nix systems "locate" needs to manually rescan the whole HD to update its database, so you can't use it to quickly find a recent file, and Spotlight on OS X is just a joke when it comes to finding a file by its name. (Or when you simply want to know where a file is)