I saw the movie on DVD a couple of months ago. Then I rented Beyond the Gates of Splendor, a movie documentary that covers the same incidents, but you get to see the real people instead of actors playing them, and they do a lot of interviews with the people involved.
But I was still interested in learning more about this remarkable story, so I checked out End of the Spear, the book, by Steve Saint, from the library. I just finished reading it last night, and I can't recommend it enough. The book mentions all sorts of things you just can't cover in a movie, and all of it was fascinating. This is truly a story of a family's relationship with the Lord and how that works out in their lives, in small and large ways, in every day situations and large life challenges. I highly recommend this book, whether you've seen the movie or not.
One other comment: the movie briefly showed some sort of supernatural vision right after the 5 missionaries were killed in 1956. This was not really explained fully and I know some critics took issue with its inclusion in the movie. I'd gotten through the whole book and it wasn't mentioned -- that was the one thing I wanted to know more about that I hadn't found out about in the book. But then I flipped the page to the Epilogue, and there it was. Steve Saint explains how the Waodani told him what they saw and why he believes that it really happened. Very fascinating and encouraging book!