Actors and actresses most might know by face, but not by name.

He’s the first person I thought of. There’s also the guy who was a generic biker character in the seventies and eighties (he was in Every Which Way But Loose).

James Hong has one of longest careers and longest imdb entries. Pretty much everyone recognizes him but few could probably name him.

Anyone familar with pre-1970s cinema and TV would immediately recognize this guy:

That one guy in that one action movie, and that girl in that show that used to be on NBC.

Margaret Hamilton, aka, the Wicked Witch of the West

If they haven’t been mentioned already…
Stephen Tobolowsky

Jon Polito

Really, the definition of “actors who everybody recognizes but nobody knows” is pretty much “actors in long-running commercial campaigns”.

For example, Morgan Smith Goodwin, aka the Wendy’s girl. Or Stephanie Courtney, known to all, hated by some, lusted over by others, as Flo.

Charles Lane

Roscoe Lee Browne

Most of these dudes always seem to end up on Law & Order, usually playing different roles, too.

Of course TV Tropes has an article on the phenomenon: http://tvtropes.org/pmwiki/pmwiki.php/Main/HeyItsThatGuy

That was The Great Santini.

He was even up for the part of Sulu: Performers considered for Star Trek roles | Memory Alpha | Fandom

This guy? He played Cal on Sanford and a biker called Animal on Rockford Files.

Bo Hopkins was in that episode too, as Jim Rockford’s buddy:

He was leader of The Pharoahs in American Graffiti, and was killed in Vietnam in the sequel.

James Hong is also the Chinese restaurant owner who can’t stand Sheldon on Big Bang Theory.

This guy I remember seeing in a lot of movies and TV shows when I was a kid, but I never knew his name. He was easy to recognize because he was tall and skinny, had a prominent Adam’s apple, and always spoke slowly and with a Southern accent.

He was in The Raid with Van Heflin; when the Confederates are putting together a covert recon team, someone asks him “Can you talk like a Yankee?” (he obviously couldn’t).

I was amazed to see that he died fairly recently (December 2011), and that he had a role as a Klingon in Star Trek VI: The Undiscovered Country.

Cracked page, also linked in TVTRopes. It’s a little old, so some are questionable nowadays. JK Simmons just got a Golden Globe but maybe he still counts. Trejo has graduated I think. Dylan Baker yes! (poor man’s William H. Macy?). Fichtner (although I think Christian Slater is a slightly poorer man’s Kevin Bacon. Slightly). Jenkins as well.

Keith David I know (like that his first listed movie is the “someone threw out a perfectly good white boy” part (swiped from Better Off Dead…). Except I have to do a Homer Simpson and write down his and David Keith’s names on my hand. And speaking of John Heard, I also have to write John Hurt = British; William Hurt = American.

No, not the guy who played Cal. The guy I’m thinking about was not as big.

John Quade is the guy I was thinking about.

Whenever a movie has a role for an irrascible but lovable old Jew you’re likely to see this gent: the late Lou Jacobi.

http://www.rottentomatoes.com/celebrity/lou_jacobi/

He was Uncle Morty in*** My Favorite Year***, the transvestite in **Everything You Always Wanted to Know About Sex, *** even one of the refugees hiding in the attic in The Diary of Anne Frank.