The Help by Kathryn Stockett spent over 100 weeks on the New York Times best-seller list.

"The Brethren" by John Grisham was on the New York Times bestseller list for 18 weeks.

The New York Time Best Seller list is generally published weekly in The New York Times Book Review magazine. It is one of the most popular gauges of book popularity in the US.

A book makes it onto the New York Times Best Seller list by how the book's sales go weekly. If a book sells well, and it shows to sell well by independent sellers, it will then make it onto the list.

I am not sure of single book, but the Harry Potter series had at least one book on the New York Times best seller list continuously for 10 years up until about 2008.