I too would do the RV thing, it will combine the rental car and hotel in one. Only drawback would be when you spend time in the east around the major cities. But most if not all have RV parks in the burbs and you can always base yourself there and use public trans or rent a small car for touring the cities.
Seeing everything in the States is a very difficult thing but a year would give you that opportunity. I would start in the North East (New England) and work your way down to maybe Washington DC, then go west. This is just my opinion and I hope I don't offend but the entire mid part of the country may well be passed over at a high rate of speed with few stops in favor of the more scenic sections such as The Badlands in South Dakota, Rocky Mountains, Grand Canyon etc. I agree that driving the west coast from north to south is the way to go. The drive on the coastal highway from SF to LA is one you simply have to experience and going south means you will be on the ocean side of the road.
[ Edit: Edited on 13-Jun-2009, at 10:35 by DaveinMD ]