Data Rescue can help you retrieve lost files, whether they were destroyed in a hard-drive crash or just accidentally deleted by some overzealous trash-emptying.
This app has an easy--and even kind of fun--interface, with 3D animations that show available drives and your options for diagnosis and recovery. Once you've chosen a drive to examine, Data Rescue prompts you for an additional drive to use as "workspace" and gives you six choices: a Quick Scan or Deep Scan to find recoverable files; a Deleted Files Scan (good for an accidental deletion on an otherwise healthy drive); Clone, which makes an exact copy of a drive, good if you suspect mechanical problems and want to do recovery on a more stable drive; Analysis, which will clock your drive's read time, a possible predictor of future problems; and FileIQ, in case you need to teach Data Rescue file types that it doesn't already recognize, such as proprietary formats.
Data Rescue is fairly speedy, scanning a removable flash drive in a few minutes or a larger hard drive in hours, with satisfying animations to keep you entertained; for example, you can see a running count of extensions for recovered files, like MP3s or AVIs, which pop up as Data Rescue finds them. Once the app is finished scanning, you'll see a complete list of recoverable files, broken down by folders such as audio, documents, and images, usually with file names and metadata still intact (depending on the extent of the file damage). From the list, you can preview files or simply recover them.
Data Rescue's demo limits you to previewing and recovering a single file of 10MB or less, but that's enough to see this app in action and get a feel for its friendly interface, good documentation, and impressive recovery capabilities. This is the kind of software that you hope you never need--but when you do, Data Rescue is a great app to have.