Filler is a simple program I use to backup partitions. It does the equivalent of a simple:
cat /dev/zero > my_file.tmp
Its interest is that if you fill a partition with zeros, then it's easier to compress it efficiently in order to make a nice .tar.gz you'll burn on a CD later. Perfectly useless under UNIX, this program becomes a must under Windows, when there's no such thing as /dev/zero by default. With this program I've been able to compress clean images of Win2K installs on a 10Gb partition, and make them fit on a single 700Mb CD.