JetBlue and Virgin are two of the best airlines to fly around the US right now. JetBlue is now offering the cheapest flights to San Francisco from Boston for $219 including all taxes and fees.
Cheap Flights from Boston to San Francisco
Just announced as part of their summer sale, Virgin America is offering one-way flights between San Francisco and Boston for $109.
May need to be flexible enough to avoid booking on certain days. May need to book two weeks in advance.