I remember one with a girl huffing glue in her bedroom, and a voice over explaining that huffing deprives the brain of oxygen and that "When you think you're sniffing, your brain thinks your drowning" as the room started to fill up with water and the girl desperatley tried to escape by swimming to the window. And it ended with; "...and your brain is pretty much right" as it showed the final shot of the girl pressed against the window, apparently dead.
It was simple and yet disturbing enough to be effective. It really spooked me as a kid.
Oh, btw Snatch, I found the one with the pot and the gun:
http://www.mediacampaign.org/multimedia/den.mov
and the one with the little kid on the bike:
http://www.mediacampaign.org/multimedia/drive_thru.mov
This one is actually fairly realistic:
http://www.mediacampaign.org/multimedia/wallet2.mov
Go here for more anti-drug commercials:
http://www.drugfreeamerica.org/Commercials/
There's actually one in there with Henry Rollins. Look under the anti-methamphetimine campaign.