I also strongly suggest that you look at private networks as a backup to your Internet access. Remember frame relay and ATM? Much of the last decade has seen organizations cut costs by bundling VoIP services, data, and VPN all over the Internet. That may be premature. Think about private circuits between your locations and your major customers/partners. Satellite links between data centers are often installed as a third level of backup connectivity. Think of that for your own networks.
And finally, as crazy as it seems, do you have any modems left? It may be prudent to invest in a bank of digital modems and give some thought to the routing architecture you will have to throw together if the public Internet fails. I remember mixing 11 modems together to support my ISP when our uplink went down in 1994. The Internet will, of course, survive any cyber attack (after all it was designed to survive a nuclear war), but it could easily suffer very disruptive outages. Mitigate the impact of those outages on your operations by thinking today about tomorrows newest threat: real war.
Richard Stiennon is a security industry analyst. He writes the security blog for ThreatChaos.com and has re-launched IT-Harvest, an independent analyst firm that researches the 1,200 IT security vendors. Most recently Richard was chief marketing officer for Fortinet, the leading UTM vendor. Prior to Fortinet he was VP of Threat Research at Webroot Software.