1. Empire Star by Samuel R. Delany
What is there to say about this book, other than Read It! Multiple overlapping time streams, multiple characters developing at multiple periods, and the books that gave us the simplex, complex and multiplex view of the world. A book that tells its story off-screen and is no less gripping for that, the time travel mechanism is an area of space compression where anyone who enters may emerge at any point in their timestream. And right up until the closing words, if you think you know what is going on, you’re wrong.
Amazon UK – Read Sample

2. End of Eternity by Isacc Asimov
One of the original time agency stories, laying out exactly why time agencies and time police are such a bad idea. Notably far darker in its handling of cause and effect than the modern versions have dared to go, and a perfect example of the road to hell being lined with good intentions.
Amazon UK – Read Sample

3. Millenium by John Varley
Air crash investogators notice something very wrong about incidents, and that is as mucha s I can say without spoiling the story. The short story Millenium was based on, called “Air Raid”, was a Phillip K. Dick award nominee.

I first encountered this in its filmed version, which is not a very good: Kris Kristoffersen and Cheryl Ladd in a comparatively low budget sci-fi flick. However what makes it notable is the two lead characters, both on different timelines, and the shot-for-shot reuse of scenes as they occur in each character’s timeline, which gives the audience a very different persepective on them. The idea of timequakes and distortions caused by paradoxes is not explored as thoroughly on screen as it might be in text, but is still an intriguing concept.
Amazon UK – Read Sample or Amazon UK (DVD)

Honorable mention: “Beep” by James Blish
Now largely only available in its longer form, “The Quincunx of Time”, this story examines the complication of instaneous interstellar communication in terms of determinism, physics and the social effects. While not strictly speaking a time travel story, it has similar effects on paradox. I’m not going to spoil it by discussing it further, because it’s a very good read. I preferred the short story, but the long form is worth a read.
The Quincunx of Time: Amazon UK – Read Sample

For Doctor Who fans? The best one for time travel physics is to my mind still Day of the Daleks (Amazon UK DVD), which handles the concept of time actually rejecting changes and incorporating the causes into the timeline to prevent paradoxes, a concept sadly dropped by the new series. And if it reminds you of terminator, this serial was written twelve years earlier.