Let me start the discussion with several:
The old standby was Will Durant's The Story of Philosophy - full of wit and wisdom, but also replete with personal prejudices and some notable omissions, including those from being published in the 1920s.
Although I am not a big fan of Russell, Bertrand's History of Western Philosophy is a good read.
One of the strangest books in the genre is Richard Tarnas's The Passion of the Western Mind. I loved it right up until half way down page 425, when, IMHO, it just went off in a rather bizarre direction.
Two good dictionary approaches are W.L Reese's Dictionary of Philosophy and Religion and also the Cambridge Dictionary of Philosophy, edited by Robert Audi.
For fuller treatment, I recommend Frederick Coppleston's scrupulously presented nine volume series "A History of Philosophy". Also recommended is the more up-to-date Routledge 10 volume series, on the History of Philosophy.
One cannot conclude this list without at least one of Mortimer Adler's books. My suggestion there would be either The Four Dimensions of Philosophy or Ten Philosophical Mistakes. Both are useful foils in dealing with the other books.
I have other recommendations, but I hope that this post will be sufficient to stimulate a fruitful discussion of the foundational second-source books on the topic.
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