Trickster is an app that provides an advanced "recent files" window that lets users track down lost files that they've been using.

An easy trick to perform

Trickster sets itself apart from other similar apps, of which there aren't many, and other "recent items" panes, with its interface. It comes in jet-black, like a magician's hat, and though that doesn't blend in with the default Aqua interface on Mac OS X, it looks nice enough. It does, however, allow the user to automate their file-finding tasks, make custom recent lists, and so forth... as long as the user knows how.

Put this one in your hat

Trickster is a great way to figure out what you did with files you recently downloaded or dug up and then lost. It improves your productivity massively even if you only lose track of files on occasion. You're still reliant on the relevant apps to open the files, even if it's something simple like a full-resolution image preview, but that's a small quibble.