Ultradefrag

For Windows users, there's quite a lot of "housekeeping" work that needs to be done that is either not necessary at all or only a very minor chore for users of other OSes such as OS X, Linux, FreeBSD and Haiku.
One of these is defragmentation which arises because of a weakness in the NTFS filesystem which allows a large proportion of stored files to be stored in parts, or fragments, which may be quite distant one from the others.
Although Windows 7 has its own native defragger, in the few times I used it, it never seemed to do very much and seemed to be underreporting the extent of fragmentation.
So I took a look at the free app Ultradefrag and it seems pretty good. A good graphical interface is presented which provides a good visual impression of the state of your HDD.
In addition to just fragmentation it provides an Optimize command which not only defraggs the HDD but also pushes almost all files to the more easily accessible outside part of the disk.