http://www.auslogics.com/disk-defrag

Auslogics Disk Defrag has been my favourite defragmenter for a long time now. It is part of my own custom "standard" tune-up procedure I run on every Windows computer that people bring to me to work on. It is fast and visually thorough, and much more efficient at defragmenting than the built-in Windows defragger. For me there is absolutely no better alternative.

Quick review from the Lifehacker website:

"Auslogics Disk Defrag is a fast and effective disk defragmenter intended to replace the Windows default. It's quick and easy to use, and Auslogics DD provides a nicely formatted report of the latest defrag, including a motivating "Defragmentation has increased this computer performance by X%" message."