Every Tuesday night at 8:00. Arguably the least useless of the televized public popularizations of science out there.
ScientificAmericanFrontiers? is pretty good, but Nova has a better track record and is on more regularly.
I have been reading ScientificAmerican since getting bored in 5th grade and picking it up in the back of the class, yet I have never seen a Nova that did not teach me something. --PhlIp