Yes, keeping an external hard drive and mirroring it on a regular basis is the best way to back up. Best to store the backup off site if it's anything really important. (what if there were a fire?).
We are prepared to live in the plain and die in the plain!
It's all about the fault tolerance. Having two/three backups is essential in my opinion. One backup would be a external hard drive, another backup would be DVD's. Just keep in mind that burned DVD's can become coasters due to disk rot over the years.
Currently what I do is I use Macrium Reflect Free (the free version of the program) to clone an image into one external drive every other week, and to another external drive every other week alternating. But I only "clone" my main HDD which is like 200 GB worth of data, hence I can do it to my two 320 GB externals without issues.