Um... there are probably lots of PSAs I saw as a kid, featuring characters like Smokey the Bear ("only you can prevent forest fires"), Woodsy Owl ("give a hoot, don't pollute"), McGruff the Crime Dog ("take a bite out of crime"), Vince and Larry (the crash test dummies, not to be confused with the band), and others. I dunno if I'll get around to looking for specific commercials featuring them. There was also a series of Canadian PSAs about wildlife, called Hinterland Who's Who. I don't remember any specifically, but I remember the background music. I'm sure plenty of the commercials can be found on YouTube. Anyway... here are some other PSAs that I find memorable...

Anti-drug/anti-smoking
Playlist (9 videos): First a 1980s "this is your brain on drugs" ad (I had a poster that says "This is your brain. This is your brain on drugs. This is your brain with a side order of bacon.") Then a 1997 ad starring Rachael Leigh Cook. (In 2017 she did a similar ad with a very different perspective.) Then "I learned it by watching you!", "C-3PO and R2-D2", "Nic (a Teen)", "Snake", 2014 anti-smoking ad "Bully", 2015 ad "Science Class", 2016 anti-drinking & driving ad featuring Helen Mirren; a 2016 anti-smoking ad featuring Anna Akana.
(I really would like to include an ad I used to see that had a charred guy smoking, but so far I can't find it.)

Environment
Here's an Arbor Day Foundation ad featuring Carly the Cardinal.

Safety
Here are a couple of commercials encouraging safety around electricity, featuring Louie the Lightning Bug. Then a nostalgic (kinda creepy) PSA featuring Astar the robot. And a fire safety ad featuring the Old Lady Who Lived in a Shoe.

In the News
A series of short news spots I remember seeing during commercial breaks on Saturday mornings, while watching cartoons in the early 80s. Here's just a taste of the theme & globe graphic: