Yahoo has a "vote for your favorite advertising icon" this week. Some good PSA characters on there, most notably Smokey the Bear. That's who I voted for, since he's a pretty big part of Americana. Even lending his name to state troopers and their hats.
Woodsy the Owl and his "give a hoot, don't pollute" were big in the 70's and early 80's. I'm not so sure that he's identifiable to today's young'uns. I always think of Woodsy and Smokey when it comes to PSA characters.
I know who you mean with the nurtional geek. Weird yellow guy who looked an over-ripe lemon. "When my git' up n' go has got up n' gone, I hanker for a hunka' cheese!". Googled around and found out that his name was "Timer". They played his spots forever. They were mid 70's stuff, but I remember seeing them in the early 90's!
This blogg-ish page has some of Timer's stuff:
http://www.vaiden.net/childhood_memories2.html(Including RealMedia files of the original spots!)
BTW, did anybody ever make one of his "wagonwheels"? Or the "you'll have a fun time eating sunshine on a stick" ice cube tray thingie? I threw a Halloween party a couple of years ago and served "wagonwheels" with Ritz crackers.