Well, the first decision is whether to take the northern route (primarily along I-80, at least in the west) or the southern route (mostly along I-10, with bits of Route 66 along the way).
A lot of this would be based on the weather when you go.. seeing as how you're doing it in the summer, either would be fine, with the southern route being *much* hotter - I'm noramlly not concerned about that, but if the car you take has a tendency to overheat.. well, you know the deal.
Also, you could take one way out and the other way back, and see MUCH more of the country that way.
There are a ton of road trip planning web sites out there where you can enter your destination and it'll give you different ways to go there, what's along the way, etc. Give it a go!