AusLogics Disk Defrag 2.0

Disk Defrag, by the Auslogics Software, will return the lost vitality of your disk drives, and it will do it in a record time. Using this program you will be able to recover the initial speed of your disk units. In fact, it is much faster than many of its competitors, even it allows you to keep using your PC during the defragmentation process.
Its best point is in its user interface, a polished environment that only shows the important stuff for you. The result is a clearer and simpler to use interface, which also means that it is more accessible to the user, whatever his/her level of knowledge is. Once the process is finished, your CPU and memory will go back to work a lot faster. You can also make it work in the background when you aren't using the PC, and it will keep your disk defragmented and ready to work.
The program is free, but you can support the developers by making a donation trough their web page. Disk Defrag works on Windows 2000, Windows XP, Windows 2003 and Windows Vista.