Here I report a list of softwares which, in my opinion, can help to find and correct problems not only on hard disks, but also on USB keys and flash disks. The main choice criteria are the computer resources consumption and the ability of performing very detailed or low level operations (that is to go beyond the usual Windows Scandisk):

1. HD Tune: a simple program for Windows which benchmarks the hard disk performances, reads SMART attributes and scans the disk surface. Really light and efficient, even if sometimes it doesn't find the problems.
2. HDD Low Level Format Tool: One of the many fantastic programs from the website hddguru.com, which helps to low level format hard disks, USB drives and flash memories. Really useful and simple. Since it formats the whole disk, included the Master Boot Record and the partitions table, after its use the disk will be totally empty. An advanced partitioning software, as GParted, is needed to recreate the fundamentals structures of a disk; the traditional Windows partitioning tool won't be enough.
3. HDDScan: another fantastic software from the hddguru.com website. It allows to low level scan the whole disk surface, according to different criteria: data integrity, reading, writing, multiple reading. It allows also to low level delete all data. Really simple and well organised, especially for the ability of queueing different operations.
4. MHDD: in my opinion the most powerful software to manage hard disks, always from hddguru.com website. Unfortunately it can't be launched from Windows, but only from DOS. We need to create a boot Floppy Disk or a boot CD-Rom with DOS. It's a software half the way between the command line and the graphical interfaces, but it contains a very well described real time help, which allows to learn its usage quickly. The software allows to perform all the tests described in the previous points: reading or writing scan, getting SMART attributes and low level formatting. Moreover, it allows to set or visualise many disk properties usually hidden, like for instance the heads noise level.
   Finally, it offers very advanced options to repair the disk. For example, we can remap automatically all the sectors of the hard drive in order not to use the damaged ones. Or we can rewrite the MBR sector with a standard DOS version, in order to fix the installation of a boot loader like GRUB. It's really a must-have tool for everyone who wants to perform really specific actions on a hard drive. Personally, many times it was really helpful to restore damaged hard disks.