I don't know that it's that hard.
http://www.paperbackswap.com/Books-Made-Movies/tag/8969/
This is one single google search that brought up nearly 400. Granted a lot of the movies weren't great, but I'd argue that a lot of those books weren't great either. And, of course, there are many, many more.
This argument usually gets brought up by "book people" that often get offended by the movies on some personal level.
I've always viewed them as two entities that each have their pluses/minuses. For example, a book will describe the scene in detail telling you the thoughts and feelings of a character, but it's up to you to imagine what that character or scene looks like. Movies are just the opposite. You are presented with the visual and you must imagine the abstract.