I believe that Techtool Pro (part of some new bundle Check it) has a hard drive tester. i'm not sure how useful this tester is though. AFAIK hard drives regularly fail to a small extent and the drive or computer marks the space as unusable. This process is not noticable to the end user. When the entire hard drive really bites it, it is usually all at once and very sudden with no warning. Some advanced systems like XServe I believe have sensors that may alert you if your hard drive is about to fail as well.
Of course you could just try copying a whole bunch of files to the drive the reformat it and do it again.
You could install SmartReporter to monitor your hard drive(s) and alert you when the SMART status of the drives indicates impending failure. You can even have it e-mail you in case you're at work and want to take action.