What hard drive/model do you have? How old is it?

Depending on the firmware on you hdd, it may have the technology to
automatically retire bad sectors and mark them for non-use. Most new hard
drives have diagnostic firmware that detects when the hard drive is failing in
several different modes.

Other than that, the fsck command as has already been pointed out is a good
place to start.

You can also download the hard drive manufacturer's diagnotic software to check
out your disk.