A lot of people here talking about the northeastern routes, but there's another good one that is kinda worth it: San Jose to Santa Barbara on the Coast Starlight, on account of SBA being very expensive to fly through. It's about 8 hours (driving is 5-6) and comparable in price to a bus (and it is probably beating gas right now, to be honest). And the tracks go by some of the prettiest coastline in the United States, usually around sunset too.