(which reminds me I haven't defrag'd my hard disk for a few weeks now :)
You may want to look at Perfect Disk by Raxco http://www.raxco.com I've been using it for several years now and it has features beyond the standard defragger that comes with Windows. It can do a boot-time defrag so that it will defrag files that are normally locked because the system is using them, also has a stealth mode so it will defrag in the background if your machine is idle. Set it and forget it.