Not forgotten from long ago and long, long ago
Suavecito by Malo
Funky Nassau - Part 1 by The Beginning of the End [1971 ?]
Expressway To Your Heart by The Soul Survivors
(Just Like) Romeo and Juliet by The Reflections [1964]
Tobacco Road by The Nashville Teens
Swinging On A Star by Big Dee Irwin (with Little Eva) [1963]
Party Lights by Claudine Clark [1962]
When we name names, you should remember that the choices are subjective to the maximum. And some part of Classic Rock's appeal (beside being great music) is based on memory of the contemporary environment. Some of the stuff that was considered experimental at the time (long, long rambling solos, especially drum solos) seem rather self-indulgent today. There have always been artists trying too hard to copycat the elements that worked for the super-groups. I suggest you dig deeply into stuff that interests you initially -- the best cuts are sometimes buried in an album behind the more commonplace.
Having said all that, here's a few noteworthies.
Jethro Tull
Steppenwolf
Grateful Dead
Jefferson Airplane
Country Joe & The Fish
Johnny Winter
The Kinks (not just "Lola" -- the Kinks are under-appreciated)
Stevie Wonder (after he took the controls from Motown)
and later on
Peter Frampton
Supertramp
I always heard it as "pumped a lot of plain" meaning regular gas as opposed to premium gasoline. That made some sort of sense to me. I guess I'm suggesting still another possiblity and adding fuel to the confusion.
It is usually 'yeah, yeah, yeah, yeah' or 'yeah, yeah, yeah, yeah, yeah', but Steve Miller uses 4 or 5 yeahs for emphasis in good percentage of his songs.
"Living in the U.S.A", "Jet Airliner", "Space Cowboy", "Your Saving Grace" are a few examples.
"Do You Know What I Mean" by Lee Micheals.
The 1971 AM hit & Top Ten single featuring Lee's wailing vocal with keyboard and drums as the only accompaniment branded Micheals a "one hit wonder" (although he recorded ten albums between 1968 and 1981).
[*] Feeling Alright - Traffic/Dave Mason used in a Friskies cat food commercial.
[*] "Do you love 3? now at Applebee's" bastardized version of the Contours classic Do You Love Me? (Now That I Can Dance).
[*] Snippet of Skynard's Sweet Home Alabama used in KFC (Kentucky? Fried Chicken) promo.