http://www.mrmoneymustache.com/the-mmm-reading-list/And don't forget to check your local library on these - be a smart cookie and take a book for a test drive before deciding if it's something that warrants a $ investment. :D
My personal top recommendation is Jim Collins' "A Simple Path to Wealth" (Amazon link is on MMM reading list) since it was a super easy to understand and entertaining read. This series (you can see it on his website too) is honestly the reason I now understand everything since it gave me the foundation on which to build from.
http://jlcollinsnh.com/stock-series/ This book/series is worth the cost of purchase, and you could totally give it as a gift to anyone else that is interested in a overall basic money/investments education. It is weighted towards being an index investor, but that's the "simple" part of the title - why complicate things when you have a legitimately easy pathway you could follow?
The Millionaire Next Door was fascinating in showing how outward trappings of wealth usually weren't all that accurate in showing who had what. But it is more for broadening your viewpoint than an instruction manual.
Other recommendation is the Bogleheads Wiki site. Not technically a book, but once you read The Simple Path to Wealth, the Bogleheads wiki will take care of any other details you might possibly come up with regarding index investing.
https://www.bogleheads.org/wiki/Main_Page