Hello ipwn3r456,
I will List 4 of the best available in the Internet, Out of these choose anyone of them.
http://www.techsupportalert.com/files/images/HDHealth_CrystalDiskInfo3.7.0a.png
CrystalDiskInfo is a great monitoring program that can warn you if the temperature or the health of your drive is deteriorating. Its default temperature warning is set to 50 °C/122 °F which can be adjusted. It offers graphs of the accumulated S.M.A.R.T. information. It had no problems telling me almost everything about my external USB hard drive. I like that it lists the Power On Count as well as the total Power On Hours. This is Open Source software. There is a portable version as well as an installer. Overall this is one of my favorites. If you choose to use the Installer you can choose to install the ASPCA browser add-on. The Portable Zip does not include anything extra.
http://www.techsupportalert.com/files/images/HDHealth_HDDScan3.3.png
HDDScan is by far an exceptional piece of software. The interface takes a little getting used to. One feature that got me excited was the Graph when you're scanning the surface for bad (unreadable) blocks of data. It lists the blocks by response time so you can see how many blocks are getting close to unreadable before the data in those blocks is lost. Even though it warns you about unchecking the box that disables the maps dynamic update. I unchecked it anyway and my system became unresponsive and even though it was still chugging along, I had to press the button.
It's also recommended not to have any other programs running at the same time you're scanning. There is also the Conveyance (travel damage) test. Excellent for when you receive a new or old internal/external hard drive in the mail or even from the store. I also liked the PM (Power Management) setting. I was able to adjust the PM on my external USB hard drive. Overall this is definitely one for my goody bag.
http://www.techsupportalert.com/files/images/HDHealth_DiskCheckup3.0.1002.png
DiskCheckup is a capable tool. It lists information about the drive as well as S.M.A.R.T. information. It has a temperature warning should your drive get to 60 °C/140 °F which can be adjusted. It can also warn you if a S.M.A.R.T. threshold has been passed. You can configure it to display a popup or it can send you a notice via email. It detected both my external as well as my internal hard drive with no problems.
On my healthy hard drives it gave me a TEC(Threshold Exceed Condition) date when the temperature got to a certain point. TEC is mostly useless because a drive has to maintain a constant in order for the date to even be valid. My hard drive does not normally stay very hot so it was largely inaccurate. A hard drive that is starting to wear out could potentially fail at any point before or after the TEC date. So in my opinion it may spook people more than anything else.
http://www.techsupportalert.com/files/images/HDHealth_HDTune2.55.png
The free version of HD Tune provides a useful benchmark to test your hard drives performance as well as a block scanner which works with both external and internal hard drives. It also lists S.M.A.R.T. and general information for internal drives only. The free version is no longer updated.
For continuous monitoring I recommend CrystalDiskInfo for its well rounded set of features. HDDScan is an exceptional diagnostic program. Both are excellent pieces of software. To ensure your drive isn't degrading in ways that may not be readily apparent with a monitoring program alone I recommend testing the surface of your drive with HDDScan, HD Tune, or the simplistic Ariolic's Disk Scanner. Kudos brother ^^