I think I'd have to agree and disagree with both of the other previous posters, more or less.
What you did was you likely had a sector go bad on your drive, so you reformatted it and during this process the bad sector got remapped to a spare sector.
Of the tools mentioned, as far as I'm concerned, Scannerz is probably the best hard drive tool on the market. It doesn't pretend to be something it isn't. It analyzes both the drive surface and mechanicals, and provides warnings that point out problems other miss. It is NOT new, it's almost 2 years old I think and I noticed it went up in price. They used to have a USB
launchable version that I guess they got rid of.
I wouldn't dismiss SMART reporting and "Smart Reporter" is, like Kurt said, a good choice. There are some SMART reporters out there that are commercial and flat out don't work. One of them actually interprets SMART data erroneously. I wouldn't be terribly alarmed if a SMART report showed some errors, but it shouldn't be misinterpreting them or reporting false errors.
A lot of the tools on the market for drives are getting really pretty old and they're outdated, and some of them appear to do nothing more than serve as interfaces to utilities that have long been on the OS. I'd say a good suite for handling problems would be:
a. Scannerz for hard drive scanning.
b. SMART Reporter for SMART evaluation
c. Disk Warrior for fixing indexing problems.
Disk Warrior hasn't been mentioned yet, and I don't even know if people still have indexing problems on their drives. I haven't for years, but some people swear by it.