Do you mean disk defragmentation or system optimizing?
For system optimizing I use Alsoft's DiskWarrior.
As for disk defragging, the jury is still out on that one. Some people claim that Unix doesn't need any disk optimizing, others say that their Macs slow down to a crawl because of disk fragmentation... It would seem like in Panther it isn't as bad as in Jaguar (10.2) and that Apple made sure that Panther would check and repair on itself a little bit better than Jag.
But rumor sites write that Tiger, the next Mac OS X generation, will contain disk defragging... So my question is... If Unix doesn't need disk defragging, why will Tiger have it then?