By better, I guess you mean more thorough or better by being able to run without having to boot from the OS X DVD that came with your iMac. Apple’s Disk Utility works well, but in order to really repair disk problems and disk permissions, you need to boot from the OS X DVD, because Disk Utility can’t do those complete repairs when actually booted from the same disk. You can boot from the DVD and Disk Utility will do a good job, and of course you need to use it to partition the hard drive for Boot Camp.
But there’s a disk utility that I use that works very well, and it’s called AppleJack. It can be run in single user mode by itself, and it repairs disk problems and file permissions and cleans caches. I’ve used it for years, and it has recently been updated to run on OS X Snow Leopard.
It’s not the usual program you’re used to running on your iMac. It’s text-based and runs in single user root mode, so you need to be careful using it. To run it, you hold down the Apple Key and the “C” key at the same time right after you hear the startup chime. It looks like this:
Read the instructions that download with it. But Applejack works very well, and I usually install it on all the Macs I work on. It can fix some errors that Apple’s Disk Utility can’t fix. And it also clears font caches and does other cleanup.
I even use Applejack on client’s machines, and if there are problems, I can talk to them on the phone and have them run Applejack, and have been able to fix problems just like that.