Yosemite is gorgeous, Death Valley is hot, dear god it is hot! Take along a roll of aluminium foil and fry eggs and burgers on a table using pure solar power - but my haribo melted in the boot so I can never return without a broken heart...
I'd avoid San Francisco, and probably LA (although a few spots are worth hunting down), but can recommend San Deigo and the coastline generally.
The Redwood parks are ok, but to be honest after you get past 'big' they aren't that attractive.
Vegas is just a few hours drive over the border, and always worth a visit.
I'd seriously consider hiring a van, hippy mobile, or recreational vehicle - the extra hire cost will easily be outpaced by the motel savings.
I went last year and can dig out the hire car places, etc, etc, I also have god knows how many photo's if anyone is interested and over in the UK
Oh wait, Santa Barbara, free internet access in the library, and a Cold Stone Creamery, there is heaven on earth, although apparently Neverland is next door so avoid the scary people.
Pick the right time of year as well - I got the June glooms so you probably want later.
