I use a bunch of external USB hard drives for imaging at work, and I've finally figured out how to steamline the process.  Clonezilla is a great tool, but it gets annoying to go through the same exact steps when you are imaging 20 machines at a remote location.  If I had more bandwidth I would look into setting up a clonezilla server, but for right now doing a external USB hard disk to internal disk clone in 20 minutes works pretty good.