In theory, it could be possible to travel to the future if you hang out on the outskirts of a black hole.
As for traveling to the past, that is a bit more complicated. Obviously no one has succeeded at it in the future so far, since they have not paid us a visit yet.
NOVA's
The Fabric of the Cosmos was a very interesting series. Of course the concepts are simplified to help people grasp them, but it still provides some great information.
Here is the segment on time: