The steel plow was a big one since the soil around the Great Plains was very rich and hard to dig up. The older iron plows would get stuck.
The water-pump windmill for storing water, since the Great Plains did not get much rain.
Railroads to the West helped people move to the West and also gave Great Plains farmers a way to ship their crops.
Barbed wire is another invention that let them build big fences without needing a lot of wood, since the Great Plains did not have much of it.
Wheat farming and the invention of the mechanical reaper.
Cattle raising techniques gave them a new business too.
There are more, but these should help you get started.
