Ben Goldacre in NYC

I've read his column in The Guardian for a few years. That, and his book, are essential reading for anyone interested in the truth behind the media interpretation of science. Most of the columns also appear on his Bad Science blog, sometimes in an extended (less sanitised) form.

He's a medical Doctor, and his writings are often aimed at medicine in particular. He really does take no prisoners... Alternative medicine or big pharma, if you haven't followed proper scientific method for your claim he'll rip it apart, although "quackery" is where he directs most of his bile. Ben comes across as a very angry man, but it's difficult to find fault with any of his arguments.

He's on that twitter: http://twitter.com/bengoldacre and there are reviews for the UK edition of his book.