As I mentioned in an earlier post, I was going to be reading Paul Boghossian's Fear of knowledge : against Relativism and Constructivism for a course I was auditing.
Boghossian's strategy is to set up the strongest versions of the claims that are supposed to support relativism. He then goes about showing why - even given their best shot - they fall short of their mark. I wont spend time rehashing his arguments, his book is short and the arguments are clear and tight, any further compression seems unnecessary - if this is the kind of thing you're interested in, then the book itself is what you want to peruse.
It's possible that philosophy mavens might take issue with parts of Boghossian's book. There are certainly some technicalities to these debates that might complicate matters - as Boghossian himself notes in annotations scattered throughout the text.
This isn't really a problem for Boghossian though - the intended audience is not necessarily philosophers, but rather educated people in general. Specifically, people who find themselves drawn to relativism or constructivism for some or other reason. These are not people who have been convinced of relativism as a consequence of years of deep immersion in epistemology, but who have, perhaps, picked up the "profound" relativistic insight from a book on cultural theory, or a course in post-colonialism. It is primarily for this kind of reader that Boghossian wrote his little book.
That having been said, there is much in here for long time students of philosophy, especially for those like myself who have grown up on the "fuzzy" side of the divide.
I'm happy to say that I can recommend the book without reservation - if you find yourself attracted to, or even endorsing, some vague form of relativism, read this book and then reconsider.