I have two weeks to travel between Austin & San Diego in October of this year (not including a few nights at both ends). We don't really have a route yet but I doubt we'll venture further North than I40 along the way.
I'd be keen to dip across the border into Mexico if possible but I'm very aware that many places are not safe.
We're English but it's not our first time roadtripping in the States (Denver -> LA last year). I'm keen to see some Americana so may head up and do a bit of Route 66 despite the warnings about it being heavily touristy.
To give you an idea of the type of thing I like, on the last road trip I was completely blown away by Arches National Park, Dead Horse Point, Colorado & Utah mountains. Less bothered about the long flat drives through Utah & Nevada ;-)
We're into independent DIY culture and are quite hippyish so any notable counter-culture stops would be high on our list of things to do...