I'm pretty sure there are many others, but if you've been searching for one of the best yet completely free HDD defrag utility for Microsoft Windows XP, Vista and 7 then Defraggler is one little app that's worth giving a try. It's true that MS Windows does come with one of her own (built into the OS) but there are both commercial and free dedicated utilities that lets you configure a lot of other options that the built-in Windows doesn't offer.
Let's have a look at some of the features of Defraggler
*. Defraggler lets you de-frag the entire HDD, partition or individual folders/files (something that MS Windows tool lacks).
*. Add Or remove files: this is again very useful since say that you have a folder filled with video files that are only there temporarily, then even if the content is fragmented, yet you can manually remove it from the list thus save some time.
*. Very user friendly window (including using colorized methods for indicating the fragmentation levels).
*. Boot-time Defrag support: If you want to achieve the best results concerning the MS Windows system partition, then this is the best method since Defraggler can move some of the locked system files, etc.
*. Change priority: You can either run it using lot of your HDD bandwidth or can defrag the HDD without slowing down it too much thus you can do something while doing it.
*. Free space defragmentation.
*. Check disk for errors.
*. Search and find files.
*. Quick defrag: This'll do a fast defragmentation (for the impatient geeks :D) but won't give the best possible results though.
*. Schedule support.
There are among the main features to mention. As said, this is only for MS Windows. If interested, you can download it from this Defraggler home page. As said, in my experience, this is one of the best HDD defrag utility that's also completely free!. Enjoy.