The first thing you want is a natural gas powered generator, not gasoline. Nothing like having to take a trip to the local gas station (presuming THEY have power) to fill up the generator every 8 hours or so. This, by definition, will make the generator a stationary unit (not on wheels, designed to be bolted down to a concrete pad).
Next, you want a generator with auto-start, auto-transfer with manual return. You want the thing to automatically kick in if the power dies, but YOU should be in control of when it decides to return to the grid. Nothing like finding out that the power died 10 minutes after you and the family left the house for a couple of days and coming back to a cold house with no power and potentially burst pipes.
Wattage - you will want at least a 5000 watt unit for whole-house use. Forget this idea of running power cords everywhere - unless you like the idea of tripping over power cords everywhere. With the transfer switch mentioned above, the generator takes the place of the grid so your internal house wiring will continue to serve it's duty.
There are several manufacturers of house generator systems. You can find low-end units at places like Home Depot or Lowes. Better units are best obtained from an electrical wholesale house.
Do yourself a huge favor here and hire a licensed electrician to do the work. It'll get done right the first time, the electrical inspector won't get excited (in a negative way) when he sees the work, and the odds of "something going wrong" go way down.
From another guy in Michigan (Westland)...