My backup "system" is two-layered. I have two D-cell powered air pumps that have AC cords. The way they work is the pumps only run if there is no power to the AC cord, so when the power goes out, the pumps turn on. I think they were about $10 each from Premium Aquatics. It's enough to keep the water circulating and oxygenated, but of course it doesn't help with lights/heat/chilling/skimming, etc.
My second layer is I have a large battery with a built-in inverter that can be recharged (or continuously charged while in use) by DC current from a car in the driveway, or from some solar panels that go with it - the whole thing is made by a company named Brunton. It probably isn't the most cost-effective solution, but I actually already had this system for powering instruments when I do field work. When I'm not out in the field, it's at home in case I need it to run the main sump pump. Of course, the time the power is out for an extended duration will end up being the time I'm working in the field with this equipment... so I have another inverter (w/o battery - just a standard inverter) that I leave at home with my wife when I'm in the field. Unless you really think you need a lot of amperage (lights, chiller, or many pumps), a car engine works just as well as a dedicated generator. You can run a car at idle for a very long time on a tank of gas.
Jeff (vol_reefer).
Since I moved to Oak Ridge, power outages haven't been an issue... Ahhhh, but I'm looking to move soon... 
(I think my sister's cell phone charger is the main-drain actually 
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