There isn't much to do, and I certainly wouldn't advise regular use of 3rd party utilities. Save your money until you need Disk Warrior--but that day will probably never come. I'd advise strongly against anything called Norton on OS X. They all might as well be named "Norton System Destroyer X."
Unix has utilities that run in the middle of the night (Unix being designed for computers that never get turned off). If you leave your Mac on overnight (every night) they'll get run. Otherwise you can run them manally from the command line. You can also get free utilities like Cocktail or MacJanitor to run them on command. Permissions is another Unix feature that needs tending too sometimes. Open Disk Utility and select your hard drive, then 'repair permissions'. There's no set interval for when to do this. I do it weekly, others do it monthly. It's all good.
Personally, I paid $9 for an app called Macaroni, which reschedules the cron jobs for when the computer is running (but I'm not using it), repairs permissions at a set time, and removes localized files. So now all my housekeeping is automated.
Here's how I look at it--Apple thinks of everything yet they didn't include a lot of disk utilities. That tells me you don't need them, and experience has shown that to be the case.