FWIW, DiskWarrior is my most frequently (albeit fortunately still rarely) used disk utility, followed by TechTool Pro's test suite, including the bad block test MMT3 mentioned. I also own Drive Genius, MacPilot, Cocktail and Data Rescue, to name only a few of the available commercial utilities. Most of the latter are only rarely used, but can be critical in certain circumstances. Fortunately, many of these utilities have trial versions that will allow you to assess if the expense might be worth your while when problems strike.
For those interested in the bottom line, it may also be good to know that with the exception of DiskWarrior, all the utilities I mentioned have in the past few years been offered as part of software bundles together with up to 10 other apps for bundle prices of around $50. The individual utilities too are occasionally offered at considerable sale discounts. You can keep abreast of many available offers with a free utility like
MacBundleWatcher.
