His series on parser combinators is one of my favorite technical articles/series on any subject. The property-based testing one is also excellent, going into some of the real practical advantages and tradeoffs of that technique.

I've been meaning to read his book for a while now, maybe it's the time. Anyway great site and I don't even know F#. Have never written a line of it, though I have used ocaml a lot so I consider F# heads comrades.