Windows only: Explorer's integrated search is fine for most things, but more powerful searches or sorting through long lists of similar files isn't exactly easy — Listary gives you hotkeys, wildcards and commands to help you quickly find anything in a folder.
In Windows Explorer, you can jump to a file by typing the first few letters of its name at any time — Listary expands on this method by adding a search box that makes this "quick search" far more powerful. It runs in the background and allows you to start typing at any time, and when you do, a search box pops up in the corner. Listary will show you items in the list that correspond to what you've typed, and you can scroll through the results with tab. You can insert wildcards with the * or ? symbol, giving you the same control you'd get with the full Windows Explorer search bar, but with much greater speed and ease. It even has a few commands, such as /cd, which will let you change directories without even taking your hands off the keyboard.
At first you may not be entirely clear on how to use it, but it just takes a few minutes to understand how it useful it can be. For example, when searching through a list of files using Listary, you have to either start with the first character of the filename or use a wildcard (like you can see I've done in the screenshot above). Similarly, getting used to the one-word autocomplete using tab takes a minute — but just like many programs that keep your hands on the keyboard (such as Quicksilver or Launchy), after just a bit of initiation, you'll find that sifting through files becomes extremely fast and easy.
Listary is available as a free version and a pro version available, but the free version has the features most of us would want to use — however, the pro version does include regular expressions and exporting list content to CVS files.
Listary is a free download, Windows only.