I use Macrium's Reflect Free Edition and it works out great. You set up an initial scheduler file and choose the drives you want (you can choose all, some or none of your drives, including your external drive(s)). Then, just schedule it for whatever time you what, however often and choose the location the back-up file should go to.
I actually used this to image my laptop's 160gb HD before I installed a 320gb drive about a year ago. It worked so well, I'm using it on all of my PC's. Then, coincidentally, my parents recently got a number of virus's, it was quicker just to restore to a few weeks prior. The process was fast & easy.