System Mechanic is a nice set of tools that will help you with regular maintenance of your system. Tools include disk clean up, fix broken shortcuts, remove duplicate files, securely delete files, clean registry, safe installer, remove invalid installed info, startup manager, Internet privacy (deletes temporary Internet files and history), and Internet speed up which tweaks your registry settings for you so you get faster connection speeds.
Download: System Mechanic v7.1.8.4 Professional ... more

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 two 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. ... more