One of the most profound examples is the Anasazi Mysteries, a trilogy by Kathleen O’Neal Gear and W. Michael Gear. One moment you’re wholly involved with prehistoric peoples of the American Southwest, the next you’re following the lives of a modern-day team of anthropologists trying to piece together the ancient clues. Both worlds were tense and engrossing. I could hardly stand for the stories to end.The other is the recently released The Sandalwood Tree by Elle Newmark. I reviewed it here http://fagan-authorspot.blogspot.com/2011/06/as-promised-sandalwood-tree.html In this case, the distance was only 90 years, 1857 and 1947, but the two worlds were significantly different nonetheless.
In both cases, the separate stories impacted each other in many startling ways, and the conclusions had the eerie effect of leaving you in both eras at once.
This is not a technique to take lightly. An author without the string of advanced degrees earned by the Gears, or the descriptive skills of Newmark, would be hard-pressed to pull it off. These writers are not only proven at their craft, but thoroughly immersed in their subject matter. If you want a riveting read, you want these books!