Built in utiilty for Windows 2000/XP. Start --> Run. Type chkdsk /r for full scan. Can also be run from recovery console. Not recmomended for diagnosing.

Hitachi / IBM - DFT "Drive Fitness Test"
Works with all manufacturers

Western Digital "Data Lifeguard"
Works with WD drives only

Maxtor "Powermax"
Works with all manufacturers

Fujitsu "FJDT"
Works with fujitsu models only

Samsung "hutil"
Samsung "es-tool" (Successor to hutil above)
Compatability unknown...

Seagate "Seatools"
Works with Seagate drives only

Toshiba - N/A
There are no tools available for Toshiba, but you may be able to use IBM or Maxtor's drive tools as well as other third party programs

Other Useful Drive Utilities

HDD Regenerator - Repair bad sectors
Repairs most bad sectors by remagnetizing the disk surface without losing your data. Works independantly of the file system, making it compatible with all PCs, operating systems and hard drives...

Active@Partition Recovery
Recovers most deleted, lost or formatted partitions.

Partition Magic
Fast and easy partitioning, Supports all Windows and most Linux file systems. Great for ignoring bad sectors and for advanced partitioning schemes.

GPL/Freeware partitioning program for use with Windows, Linux, FreeBSD and more. Not much on eye candy, but it works. .

GPL/Freeware partitioning program for use with Windows and Linux. Nice, intuitive interface and comes available as a bootable CD image..

Acronis Partition Expert
Easy to use interface. Supports Windows and Linux partitions.

Drive Backup Tools

Symantec Norton Ghost
Ghost 8.0 or less runs under DOS, but extremely reliable. Ghost 9.0 and 10 requires Windows 2000 or XP. 9.0 & 10 are Windows-centric. Ghost 9+ supports full "hot imaging" of system partitions while in Windows, but not incremental imaging.

Acronis True Image
Supports Windows and Linux file systems. Allows "hot imaging" of system partitions while in Windows, supporting full and incremental (fast) backups. TI 10 has been rock solid for me -- Recommended.

Drive Secure Erase Utilities

Darik's Boot and Nuke
Securley erases all data on your harddrives, beyond the point of possible recovery. Use with care! Tip: remove harddrives you will not be erasing from the computer.