Free (released under the GNU General Public License) disk defragment and optimize utility for Windows 2000/2003/XP/Vista/X64. Completely automatic and very easy to use, fast, low overhead, with several optimization strategies, and can handle floppies and USB disks/sticks. Included are a Windows version, a commandline version (for scheduling by the task scheduler or for use from administrator scripts), a screensaver version, a DLL library (for use from programming languages), and versions for Windows X64.

Jeroen Kessels Software (http://www.kessels.com/JkDefrag/)

This is a nifty program, though you don't get any options once you open it, it just starts, via GUI. The meter (percentage counter) isn't accurate on some phases (I noticed the second and third phase), which is really the only thing that i've noticed so far that isn't right. All in all it's a small little program, small enough for me to download on dialup, and it seems to do a really good job.