This particular take on the cloning process is more like a bootable Linux distribution that can do bit-by-bit copying, and it supports a ton of file systems. There's an unattended mode and multicast support built in. Clonezilla SE can clone 40 machines at once. Clonezilla does use a curses-based interface, so some might find it a bit challenging at first.
Macrium Reflect Free Edition
Only for Windows file systems, but it does it quite well and has a fairly straightforward user interface. This software does disk imaging and disk cloning, allows you to access images from the file manager, creates a Linux rescue CD.
Runtime DriveImage XML
DriveImage XML uses Microsoft VSS to create images and does so with reliability you might not expect in a free tool. With DriveImage XML you can create "hot" images from a disk already in use. Images are stored in XML files, so you can access them from any supporting third-party software. DriveImage XML can also restore an image to a machine without the need for a reboot.
Runtime Shadow Copy
With this tool there is little more to do than decide what you want to image and where you want to image it to. Shadow Copy makes use of VSS so you can even copy locked files on a running system. You can copy a single file or an entire system with the click of the mouse.
Paragon Backup & Recovery Free
Is for stand-alone Windows machines, and it does a great job of handling scheduled imaging. The free version is based on the powerful pro version, but it's for personal use only. I highly recommend using the free version to try out the software.