Disk checking tools

The mighty SpinRite is the way to go.
http://www.grc.com/sr/spinrite.htm

However, it's not free.

Some other options include:

DiskCheckup
http://www.passmark.com/products/diskcheckup.htm

HDD Health
http://www.panterasoft.com/

S.M.A.R.T. Monitoring Tools
http://sourceforge.net/projects/smartmontools/

HD Tune
http://www.hdtune.com/