I'm not sure exactly what the terminology is, as everyone seems to call it different things. Was told to find a dns failover solution for our sites and a few of our customer sites and after a few hours of hunting all I managed to find was costly solutions from the usual names. We wanted something cheap, effective and 100% stable. Any way, I stumbled upon dnstrouble.com which is actually a sister site to the VPS provider I use. They offer a free dns failover solution for up to 5 domains, beyond this it goes to a business tariff, but for the average joe I think this is pretty dam good!
Any way, thought you guys might want to know about this, as its totally free and I've been using it for a while and its dam good and easy to use!