Useful HardDrive diagnostic & rescue tools
I have found following tools very useful on recovering data on broken hard drives.
With MHDD its possible to “fix” damaged blocks on hard-drive, often its needed to use methods which is destructive for the data on but it makes it possible to run chkdsk or just make image out of damaged drive to new one. I have often managed to save all the important data and quite often even whole operating system with help from MHDD 
Lost partition tables, boot blocks etc? This is very usefull tool on fixing and analyzing such problems.
Very nice collections on linux tools on rescuing data, its able to mount ntfs partitions with write support. It has also virus scanners and such. Very powerful tool, but doesn’t have any kind of GUI so it’s not for the people who a afraid of console and keyboard 
Windows PE environment useful for fixing basic file system errors, quite usefull when build with lots of driver support.
Must have tool for diagnostics, it contains a lot of tools like HDD manufacturers diagnostic tools, memory testers, partition tools, system tools etc etc. Must have tool for everyone who repairs computer related problems. It also contains small linux rescue environment called INSERT, but its optional.
Live linux cd with full GUI.