PartedMagic
UPDATE: since circa 2014, PartedMagic is no longer free to download, although still technically FOSS (in the sense that you can build it from source).
PartedMagic is a free (FOSS actually) Linux-based tool that can perform almost any operations with disk drives, including copying, resizing and moving partitions. It can be booted from CD, USB flash drive or network and is very small (around 70 MB).
Adding to the above answer as "PartedMagic is FOSS now".
I would recommend an easy to use cloning software, aomei backupper standard.
It has an easy to use interface and can clone your disks in just a few clicks.