Good summary by Cloud Driver. The route he describes includes US 26, going southeast by Guernsey SP and Scotts Bluff, Nebraska, connecting to I-80 around Ogallala, Nebraska, and I highly recommend it. Good road, not that many towns along the way to slow you down, and some interesting sights along the way. And yep, pretty much corn & soybeans along I-80 from at least Grand Island east. :) There are some neat pioneer-related sites in Nebraska, clustered around Kearney (Ft Kearny, previously mentioned, and the big arch across I-80 which includes a delightful museum about the westward movement) and Grand Island - York (Stuhr Museum of the Prairie Pioneer, for example).