I use JK Defrag now, but I'm on XP. It may work for Vista though. Its free, and seems to do a good job.
It even looks at your most used programs, and other things, and changes the order based on this.
so you guys were mentioning that the XP defrag isnt very good, what where the ones you used instead of them because that is currently all I have and I dont plan on going to vista for atleast a little while longer.