I've used mkCDrec for bare-metal, disaster recovery type of restores. It's FOSS and, once you get the dependencies worked out, pretty simple. It's command-line, so it's easy to setup in a bash script and throw in your crontab. Basically, it just makes a an ISO, or a series of ISOs, depending on the size of your server and if you use DVDs or not. You burn those to disk and just boot off the first one, run one shell script and follow the instructions. It was amazingly easy, really.
I wrote a brief review of it on my blog back in the day, here:
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