Ok, so I probably know more about America from off the telly than the two weeks total I have spent there, but my sister Tania lived there for a year and has given a lot of help for this section.
Gettin' around is going to cost you a bit if you want to see even a small bit of the country. Apparently the trains make you homesick for Railtrack, although flying can be cheaper if you want to go intercity without all the Thelma and Louise style views.
Greyhound coaches and the like will get you where you want to go, and tour companies such as Green Turtle will show you all the bits and bobs.
Another way to go, for only the price of your gas, is to deliver a car. Tania tried this- a guy on one side of the US buys a car from a guy on the other side. He doesn't want to pay delivery costs....you don't want to buy a car....you see the way this is going? Then you get to see all the bits that you want. And in Tan's case, you get to do it in midsummer without air conditioning.