"Portable" becomes a formality of sorts when you're talking about monsters like Generac's 363-pound GP15000E (*Est. $2320) and 390-pound GP17500E (*Est. $2,700). Yes, they both have wheels and handles, but you'll want a floor jack to assemble them, and moving them any distance requires a trailer or a lot of muscle.
The trade-off for that massive weight is massive power. The GP15000E is rated for 15,000 watts, with surges of up to 22,500; the GP17500E offers 17,500 continuous watts and surges of up to 26,250. One of these generators can easily power an entire house, running central air conditioners and geothermal heat pumps. The downside is they come with the noise levels to match and burn more than a gallon of gas per hour, so they're reasonable options only if you actually need and use their full power capability.
For less extreme needs, generators like the 7,500-watt Generac GP7500E (*Est. $1,000), the 7,000-watt Briggs & Stratton 30470 (*Est. $1,000) and the 8,000-watt Briggs & Stratton 30471 (*Est. $1,250) offer more than enough juice to power wells, sewage and sump pumps; hot water heaters; refrigerators and freezers; and many air conditioning units. One Sears.com reviewer says his 30470, which surges up to 8,750 watts, powered five homes during a five-day blackout.
These 7,000- to 8,000-watt models typically burn less than a gallon of gas per hour but are still noisy; one user calls the 30470 noisier than a leaf blower. Still, you might be able to get away with using one of them if there's plenty of room between houses, especially if you throw your neighbor an extension cord. Both Briggs & Stratton models have automatic voltage regulation that makes them safe for use with electronics. Even though they both weigh about 250 pounds, they're surprisingly well balanced and maneuverable. None of the large generators we evaluate comply with California Air Resources Board (CARB) regulations.