For me, digital photos. In the old days you'd you'd shoot off a roll of two of 36 when you go on holiday, and then get them developed and put them in an album. These days I'll take hundreds (most of them will be crap) on a week away. I've got GB's of the things, and use them as screensaver as well as having a digital photo frame.
PC backs up to a NAS (WD Mybook), which I don't consider to be a proper backup as it's still vulnerable to fire/theft/flood/virus, and then I back up every so often to a USB hard drive that I store at work.