The Inverter generator is a relatively new adddition to the Yamaha line of Generators. They make several models starting with a 900 watt unit going up to a pair of 2,800/3,000 watt units. These generators are selling well so I expect Yamaha will be adding higher capacity Inverter generators. Any of the Inverter Yamaha Generators will have an "i" in their model number.
The main advantages to Inverter generators is they use less gas, weigh less, produce cleaner electricity and are quieter during use.
Yamaha EF1000iS - 900 Watt Inverter Generator
Yamaha EF2000iS - 1600 Watt Inverter Generator
Yamaha EF2400iSHC - 2000 Watt Inverter Generator
Yamaha EF2800iM - 2500 Watt Portable Inverter Generator
Yamaha EF3000iSEJ - 2800 Watt Electric Start Inverter Generator
Yamaha EF3000iSEB - 2800 Watt Inverter Generator w/ Boost Technology
The Yamaha Inverters start at about $800 and go up to about $2300.