Not free, but I use Acronis True Image and back it up across the network to a USB External Hard Drive I keep plugged into my HTPC. The nice thing is that each PC has Acronis on it and each one can read the saved images of the others. Makes pulling out individual files much easier.
I recently accidently deleted 100 pictures by deleting the folder they were in. I just went to my last backup and they were there waiting for me.