Siracusa's OS X reviews, and Jon Stokes' excellent explanations of computer hardware, will both be tough to beat. Ars had some truly amazing stuff in the mid 2000s.
Those two were actually mixed up in my head and for the first however many episodes of Hypercritical I thought I was listening to the guy whose book on CPUs I was thinking of buying. Siracusa was entertaining enough that I didn't mind when I realised, and have listened to him since!