What generator should we buy?

You need to give more info like

How long is power likely to be off ?

What is the total load of your heat pads ?

How well are the vivariums insulated ?

If you have very well-insulated containers for your lizards inside the home, you're not going to need a lot of heat. If the lizard homes are outside they'll need a lot more power to keep them warm.

If they are inside, I think it's likely that a small suitcase generator will be enough, Honda has a 750 watt model which is good quality.

If I wouldn't mind spending the money I'd get this one:

http://powerequipment.honda.com/generators/models/...

Though you will have to see what your lamps and heating pads need as far as power goes. But I do think it should be more than sufficient.

Though I do not have personal experience with it. My only real experience is that I've seen on festivals people with such Honda generators and they are by far the most quiet ones. Even though you should run a generator outside for ventilation noise is a major consideration for me.

There is a larger version too. Buying used on Craig's list might be an option if you have time. I doubt there will be a lot on offer, but occasionally one might come up.

Keep in mind that you should run generators at least twice a year.

they come in all prices. My question to you would be how much yard do you have and how safe is your area as a generator might get stolen (as it sits outdoors). You can't use a generator from your garage you know. I have no idea but you might have to report that you have one to your insurance company. Why not call a public place that has several reptiles already and ask them for some tips.

There are multiple on line load calculates for generators out there. Goggle, take a peek, learn a bit so you can figure out what your load/watt requirements are. Then take a look at what is available in the area you need and do some research on those particular models. You'll also need to figure out how you plan to run your stuff, extension cords or tapping into your power supply and such. If the later, that comes with a whole slew of other issues like being able to isolate from the main grid and such. The big box stores have some decent residential units and such but you really need to figure out your watt needs first, before takeing a peek at actual units.

I put in a whole house generator that runs off the natural gas when the electricity goes out. It's sad that you are more concerned about a lizard than heating the house for yourself or saving all the food in the fridge. Your priorities need a good review.