I'm personally a big fan of Raxco's PerfectDisk for my defragmenting needs, but if you don't want to spend any money but still aren't satisfied with Windows' built-in options, this thread on Lfehacker has some good suggestions. To begin with, DirMS is a free app that comes in GUI and command line versions. The GUI is, to put it mildly, austere, but it works. At the same web site you'll find an app called Buzzsaw that defragments "on-the-fly," i.e. it detects file fragmentation as it happens and undoes it when you've got spare processor cycles. Then there's Sysinternals' Contig, which is free and command line only, but if you need a GUI for it there's a free front-end for it called Power Defragmenter from eXcessive Software. A number of posters also dig O&O Defrag, which is in the same price range as PerfectDisk, but Major Geeks has a freeware version available for download. A lot of great suggestions there. What's your defrag solution?