I didn't "go for" Cosmos, probably because I was already a cynical teenager and thought all that soft-focus american stuff was beneath me. However I did get a big kick out of Sagan's Royal Institution Christmas Lectures (in 1977, according to Wikipedia). I also heard him talk about Nuclear Winter at Cambridge. I don't know how well nuclear winter bears up as a theory today - probably the end of the Cold War has diminished interest in it - but I can't say I ever understood the excitement about it. I already had just about grasped that global thermonuclear war would be a bad thing, so the prospect that the barren radioactive wasteland which would follow would also be frozen solid didn't seem that significant.