His posts on manual calculation are pretty interesting. That's stuff like finger math, abaci, and slide rules. The abacus is a surprisingly powerful instrument—did you know that you can calculate square roots using only an abacus? His posts about the slide rule show how clever the principle behind it is (who knew logarithms actually had a practical use?). BTW, from the comments I also found a cool little post by someone else about the Kane Dead Reckoning Computer, basically a circular slide rule specialized for use by pilots (it can be used to calculate things like fuel consumption, airspeed corrections, drift correction, unit conversions, wind/plane velocity problems, etc...not bad for what's basically just a couple of wheels!)
His posts on abaci, and one on number bases, have prompted me to give more thought to how my concultures work with math. I'm leaning towards giving one of my concultures a tridecimal (base-30) number system, and possibly playing with mixed-base systems.
He's a skeptic. The bad math part of his blog is devoted to debunking nonsense, with an emphasis on skewering the erroneous mathematical arguments used by shovelers of bullshit such as pseudo-physicists, numerologists, HIV deniers, and (animal_co should enjoy this) creationists and IDiots. His post "Messing With Big Numbers: Using Probability Badly", which explains the various ways that true believers mangle statistics to "support" their arguments, should be required reading for anyone who has to deal with these people.
He's also a computer scientist, with an (unhealthy) interest in pathological languages. One recent post describes ALPACA, a language for describing (IOW programming) cellular automata. ALPACA itself isn't pathological (it's actually quite straightforward and readable), and the post itself contains a very clear explanation of CAs. But one of the examples he gives is an imlementation of a Brainfuck variant as a cellular automaton written in ALPACA. Oy!