Diskeeper 10

Formerly Executive Software International now Diskeeper Corporation has released Diskeeper 10. This awesome software package allows “Set It and Forget It”® Simplicity, which translates to the automatic scheduling of disk deframentation.
A lite version of the technology is bundled within Microsoft's latest OSes (AFAIK starting with Windows 2000). If you want the real deal and x64 support check it out.

This is a personal endorsement not a paid advertisement. I find the software useful.