Chesapeake, by James Michener. It tells the history of the Chesapeake Bay area, from the Native Americans through Watergate. It's a wonderful history lesson told in the form of fascinating stories. The book is long - over 1,000 pages, I think. I've re-read it several times!
I'm sure one reason I love the novel so much is because I love the ocean, the tides, and the marshes.
One of my many favorites is the Earth Children Series by Jean Auel (Clan of the Cave Bear, Valley of Horses, etc.). All the books are awesome. The books were so well researched and very written. The main character, Ayla is an incredible character. Her strength and determination are amazing. She is such an inspirational heroine and phenomenal woman (for a ficticious character).