Apart from The Guardian not knowing their en dashes from their em dashes, I cannot recommend this book highly enough for anyone interested in the written English language.
"Guardian Style will help you distinguish between the so-called rules of grammar that are an aid to good writing and those that you can cheerfully ignore. It is also a mine of information about everything from spelling to punctuation, from commonly misused words to foreign terms and expressions. If you're not sure what the difference is between principle and principal, if you have ever been puzzled by the rules governing the use of that and which, or if you are unsure as to whether brackets and parentheses are the same thing, then this superbly straightforward and straight-talking reference guide is for you."
It is not as pedantic and dry as it may sound. That said, don't expect the grammar on this blog to be perfect as a result. Available here.