Warning: This post includes a spoiler to Harry Potter and the Prisoner of Azkaban. If you have not seen or read it and wish to keep the surprise, stop reading now.
Michele of A Small Victory is waxing poetic about the concepts included in a novel called Time After Time. The key concept being that the past is never truly gone, that it exists side by side with the present. Toss in that the future is here as opposed to being somewhere not yet here, and you have a full picture of Einstein's space-time. The image that I like is that all of the pages of the Book of Days has already been written. While the present for the characters in a book is whatever page you happen to be on, the pages that you have read, have not read, the events those pages carry still exist.
Quantum Leap had a good start on this approach to time. All moments touch on one another. If time travel is possible, then it would only be a matter of disconnecting oneself from one "point" in time in favor of another. It fell apart with the idea that there could be a before and after a change to a time line. If there is only one time line, then there is no where outside of that can contain the concepts of "before" and "after".
The best example I have seen in popular entertainment of time travel has been Harry Potter and the Prisoner of Azkaban. The events of that final afternoon happened exactly the same for Harry and Hermione both times they were there, the only difference being their perspective. How they influenced the world in the second go-round (tossing the rock, howling like a wolf, summoning the Patronus) were already manifested for the first go-round. All influences time travelers have or "will" make to our past must have already happened. If it is in the past, it must have already happened because their isn't another schedule to place it on.