This is a blatant plug, for which I'm not ashamed. I'm on month two with the $9.99 service (1st month was a free trial), and I recommend it for anyone who reads a lot. I've been reading almost 3 books per week since I got it. In fact, I just found another good book in the 600,000 title collection: The Second Ship by Richard Phillips.
Here are a couple of others I plowed through on Kindle Unlimited, but there are many more I'm forgetting: The Atlantis Gene and the two sequels by Riddle, and all Michael Lewis books (yes, all of them). His Flash Boys blew me away. Fantastic.
The program offers unlimited reading of the titles on the list. Most current best-sellers are not included, but there are still tons of great books available. As a reader, it was an easy thing to do. It's like an all-you-can-eat buffet, except I'm not getting fat.