Defraggler is a free Defragmentation tool which will help you to defrag only the files that you require. Generally all the defragmentation tools try to process your whole drive. But with the help of Defraggler you can defragment only those files which you feel are necessary. Suppose if you use Photoshop a lot then you can only defragment those files.
I recommend Defraggler because it is 100% free. Defraggler is a single EXE application and is portable. So you can actually carry it in your pen drive and use it anywhere. The file size is also less than 1MB. Defraggler works on Windows 2000, 2003, XP and Vista. Defraggler supports both FAT32 and NTFS file systems. Moreover it works on both 32Bit and 64Bit machines.