I recently made a nice find at a bookstore's discount table, picking up a 200-page volume entitled 50 Physics Ideas You Really Need to Know, by Joanne Baker. The book actually is a quite recent release (August 2007) for it to be available at reduced price.
From Newtonian motion to contemporary topics such as the standard model of particle physics, string theory, and dark matter, 50 Ideas covers a wide range. This PDF pamphlet on the book from its publisher lists all 50 of the topics.
I've now read several of the entries. The one on Feynman diagrams is the clearest exposition I've seen of them. The (separate) entries on nuclear fission and fusion are also quite informative.