Dr. John (his 'Gumbo' album has some good songs on it that would qualify). Gris-Gris is excellent, too, but possibly too psych/weird?)
Spirit (a bunch of good songs, across the four "main sequence" albums. 'Taurus' is the song that Led Zeppelin sued over, so there's a story behind it to talk about on the radio)
The Nazz (Hello It's Me; Open Your Eyes)
King Crimson (21st Century Schizoid Man is probably the most "classic rock" of their better known 1970s stuff, but the title track or Epitaph works, too).
Tim Buckley (there's material on those first two albums that would work)
Electric Flag (their version of Killing Floor is great, and there are some other potential picks from the debut album) .
The Stooges (I Wanna Be Your Dog, Search and Destroy (possibly ruined by being in that car commercial), Down on the Street Loose)
Anything by the Velvet Underground
DID YOU KNOW that although Frank Zappa did have one album chart in the top 20 (Apostrophe went to No. 10), the Mothers of Invention did not? I would suggest Trouble Every Day or My Guitar Wants to Kill Your Mama.