I just finished reading Heavy Words, Lightly Thrown: The Reasons Behind the Rhyme by Chris Roberts. It started life as a self-published book in the UK, but is now a Gotham Books edition in the US. It's very much British, but the author has included a "glossary" to help get past the UK colloquialisms. (Interestingly, the glossary is presented in the order in which the terms appear in the main text. Sort of like end notes, but not numbered. I found it quaint, and awkward to use at times.)
Anyway, it's a fun book because is features researched speculation about the origin and meaning behind many nursery rhymes. ("researched speculation?!" I just made that up. Hell, nobody knows for certain what these things are supposed to mean, if anything. But it doesn't appear that Roberts is pulling this stuff out of his arse.)
If you at all enjoy learning about hidden meanings, or lost history, I think you'll enjoy this book. It's a quick read, and quite enjoyable.