So we're headed to the States. Where should we go and what should we do?

Fellow Australian jelly, bluemukaki and myself will be flying into LA later this year. We will have limited funds and will be basically backpacking across the country. We have a rough outline of a plan:
LA → SF → split up, I go → Davis → Portland, angus goes → Vancouver → Yellowstone → we both meet up in NY → VA → DC → Boston → then on to Europe(?).
So. Does anyone have any advice on how to execute this plan the most efficient way possible?
Got any recommendations for things to see and do in these places?
Got any tips on where the best places to stay are? (think really low budget!)
Anywhere we’ve missed that we really really should go?
Any other advice?
Anyone know anything about which visas we should get?
How is the public transport system?
And, most importantly, does anyone want to meet up?!