Time travel is a major premise for a lot of t.v. shows. To qualify for this list, a major theme of the show has to be time travel, not one episode (or even multiple episodes, a la the Star Trek franchise).
Married to the Mob, he righted the wrong and saved the day, only to leap into another time and body he knew nothing about. Most memorable were when he leapt into himself as a kid. And the one where he encouraged a young Steven King; that was pretty cool.
longest running and most successful sci-fi show of all time, and has a total of over 780 episodes, so don't take my word for it.
Sorry Sliders fans, I didn't feel comfortable including the show since it jumped to alternate realities where sometimes things seemed like they were in the past or future, rather than actually going to the past or future. The show just didn't fit the criteria.