What are you trying to find out specifically?
The very large majority of Agas in the USA are gas fired (either Natural or Propane) and either direct vent or regular chimney vent. They are sold in 2 oven models (about 39 inches wide) or four oven models (about 59 inches wide). More recently, three oven versions have been introduced. There are also electric versions which use a 2.5Kw element to do the same thing as the gas burner or small coal fire; it would be fiendishly expensive to run here in Connecticut.
While many Agas in the UK and europe heat the domestic hot water via a gravity circulating open system with a tank installed above the aga, this version has not been imported to this country. Rayburn cook stoves can do central heating as well, but only up to about 40K-50K btus from the coal/wood versions, and none of these (to my knowledge) were ever imported to the US. The only agas that do central heating are matching, separate boilers (in coal, oil, or gas) which bolt on along side of the regular aga. Like this:
There are privately imported agas of other versions in the US, the original (and most efficient) fuel is coal (anthracite or coke). I assume there are oil fired ones as well, but they burn a lot of oil (atmospheric burners) and require kerosene and very frequent cleanings of the internals.
So when shopping, you want to see if the aga has a chimney or if it just vents through the wall, how many ovens it has, and what kind of fuel it's using. Keep in mind that they cannot be moved in one piece, they are disassembled and reconstructed at the new site. Not a big deal, but a fairly complex and time consuming process.
You might want to get in touch with an Aga installer, who can help you with all of this. I spoke to Wayne Adams in Pennsylvania (againstallations.com) a year or two ago. He had lots of used stoves in stock and even had a very cool early 1930s coal fired version.
Finally, if you want to play with one, I was at the Holloway's appliance in Simsbury last week and their aga was running. It's one of the large 4 oven models, gas fired, and gives you a sense of how much heat they give off to the room and what the ovens are like, etc.