Windows 7 : Disk Defragmenter
Windows Disk Defragmenter is a computer program included in Microsoft Windows designed to increase access speed (and sometimes increase the amount of usable space) by rearranging files stored on a disk to occupy contiguous storage locations, or defragmenting. The purpose is to optimize the time it takes to read and write files to/from the disk by minimizing head travel time and maximizing the transfer rate.
Check out the GUI @ Windows 7
Microsoft removed the graphic display totally from the Vista defragger, which makes it difficult to actually see what its doing, how much the defrag has progressed etc. I use Diskeeper in automatic mode, its faster and also has a great GUI.