There's hundreds of differant gen sets that will do it.
First someone has to calulate all the loads you plan on running.
One big enough to run a central A/C system will not be cheap and most likly will cost as much as the unit to install if done right.
Do you already have gas avalible in the home? (propane or Natural gas)
In most cases it will need a permit to be install and be installed by licenced contractors.