Tau Zero by Poul Anderson is another one on the same line; a Bussard ramjet damaged such that it couldn't turn around. Because the Bussard ramjet provides both propulsion and radiation/particle shielding, they can't turn it off, so just get faster and faster...
Another one: The World at the End of Time, Frederik Pohl. A star being ("Wan-To") accelerates another star indefinitely, dragging its (inhabited) system with it.
