I like hearing how everyone prefers to do it. I have a few hard drives from old computers and I'm about to shrink the partitions, create images of each partition (using dd) and just cram all the iso's onto my backup drive. Although, I have recently wondered if there's a way to include parity bits for error correction, since you often hear of data rot stories (started happening to one of my drives, that's what caused me to do this)
Create an image, or series of images, in a folder off on another drive.
On whatever schedule you wish.
That's what I use, anyway.