Do you backup your data? How often? All of it? Unless you spoke in BASH as your baby language (because your mom was maintaining a Beowulf computing cluster on Saturday evenings,) backups will remain an elusive problem. If you are emotionally attached to what's on your hard disk, there are some very good chances that it can complain loudly when it's about to die and you get a chance to backup your data without having to bother with any data recovery mess.

Modern mechanical hard disks have an internal diagnostic system known as S.M.A.R.T. (stands for Self-Monitoring, Analysis, and Reporting Technology.) It keeps track of a number of "attributes" that could be indicating how your drive is aging, or if something in there is about to fail (see here for a mortal-friendly explanation of these attributes.)

There are programs that designed to communicate with your hard disk and uncover these attributes. I don't use Windows or OS X and so I can't really recommend any programs for these operating systems. Wikipedia has a nice list of such programs (the actual links to each is in the vendor row, bottom of the page). There seems to be a nice one for OS X here. On GNU/Linux (like Ubuntu, for example) there's the command-line-based smartmontools (see this article) or, if you'd like a GUI, check GSmartCtrl. It would be nice if somebody recommends one for Windows in the comments.

That's all folks. Take care of your hard disks.