There have been many in the 'Don't do this or that' genre, but the one that gets me every time is when the young girl is talking about her Dad having lung cancer and they say about being brave. I have tears in my eyes now, thinking about it.
There was one a while back about Paedopiles. There was a man in it and he was pretending to be a young boy. There was a childs voice as the voice over, it really dawned on me how easy it is to contact children on the net and pretend your somone else.
That one about smoking around children is really bad. And it has "Twinkle Twinkle Little Star" playing, and when the kids breathe smoke comes from their mouths, thats a really powerful message
There was one a few years ago which REALLY shocked me. it was shown on 'Tarrant On TV' and it was about leaving sharp objects around the home and it had a baby playing with a knife, laughing away as babies do and he picks it up and puts the blade of the knife in his mouth, sucking on it then pulls it out and as he pulls it out, he gives out a huge scream as the blade slices the babies mouth open.
There was an advert once about child abuse which featured an abusive father beating the snot out of a cartoon character (the cartoon character was portraying his son). After he was done beating him, the camera came back to the child but they were showing the real boy in a crumpled heap rather than the cartoon. Harrowing stuff.