If you need to defragment multiple hard drives or partitions (maybe doing something else in the meanwhile) and you want to have a well defragmented hard drive, you can try DefragDrives, an alternative to the standard Windows interface.

TweakPrefetch is an utility coded in VB.net capable of managing fetching in Windows XP, Vista and 7. It allows the user to set separate parameters for Prefetch and Superfetch. It also includes a clear prefetch data function.

HideApp is an utility coded in VB.net capable of generating shortcuts which will start your applications (bat, exe or com) in background, thus without any on-screen console nor interface.