Lately I've become hooked on Good Eats With Alton Brown on the Food Network. It's not the usual cooking show with a Chef hamming it up in front of a salivating studio audience -- it's more like a wacked-out food documentary. Alton Brown doesn't just tell you the what of cooking, he tells you the how and why and the pronunciation and folklore and science and the competing theories... and on and on. It's like a TV version of Harold McGee's classic On Food and Cooking, which believe me, is high praise.
I'm definitely a foodie, so maybe I'm biased -- but I can't think of a show on TV that is simultaneously as educational and entertaining. (And since I'm on a food tear, check out how Pixar got the kitchen stuff right in Ratatouille.)