Plus 1's for everyone as far as I'm concerned. A good question and two good answers.
I'd like, however, to emphasize the following quote from Bob O:
Steer clear of any tool that tells you it's going to take a bad sector and "repair" it. There's no such thing. That's a dishonest marketing trick that has it's roots back in the 1980's when drives were using MFM and developers could actually gain access to the drive directly, and even then, it was at best only sort of possible to do it. Those days disappeared with IDE when the controller was put right on the HD. Scannerz, for example, has an option to re-map sectors, but a warning will flash up telling you not to do it and that any information in the bad block is already basically dead, and the manual has a warning about a page and a half long, once again, basically telling you not to kid yourself.
Drive recovery can be done, with some very, very expensive equipment and people with proper training. Any application that tells you it's going to turn a failed sector into a working sector without this type of equipment is flat out lying.
As far as S.M.A.R.T. monitoring goes, there's free download called "smartmontools" that you can get from the web. There are a few applications out there that basically, as far as I'm concerned, steal the work of the "smartmontools" people, put a GUI front end on it, and then sell it. They don't make it clear that it's a free tool, and they often don't even keep it up to date. Typically they store the binary in the application's folder under Contents->Resources and it will have the name "smartctl". You can check the version by navigating to that folder and typing "smartctl -v" and it will tell you which version they're using. Odds are, it's at least 6 months or more old.
You can get the real smartmontools at the following link:
It's a command line application, but it's at least as up to date as you can get.
Is S.M.A.R.T. a good testing concept ? Well, yes and no. The unfortunate thing about it is it will only recognize problems after the fact. It's sort of like a weather man that shows up to your house after a severe wind storm did damage and announces that a severe wind storm just did some damage. The thresholds are too lenient and often won't predict drive damage properly. Scannerz measures timing artifacts via relative performance indices, and based on a post I read recently in Ars Technica, apparently it's picking up more than S.M.A.R.T. is.
A word of warning about Scannerz: They say to stop all other user programs running other than their own, and they mean it. You can't start a scan on a drive and then start simultaneously download and watch a video or a news show or whatever. It will catch every little timing oddity and report it as an error. I suppose a super high speed system like the new Mac Pro's may not be that influenced by that, but my poor little systems will! I'm not that rich!