You mean separately, or should they just change actresses mid-episode and nobody mention it?
Zack Johnson, Penny’s ex lunkhead boyfriend, played by Brian Thomas Smith. He cracks me up with the way he delivers nonsense with certainty.
Bob Newhart said my favorite line in response to Sheldon’s affirmation that he’s his Obi-Wan. “I-I’m not familiar with that term. Is that an internet?” It resonates with me, and that’s what’s important.
Raj’s parents, when they confronted Leonard on Skype about Priya. First time Leonard was ever considered a “bad boy,” from the other side of the planet at that.
I expected more from Katey Sagal and Jack MacBrayer, but that episode had too many guest stars to properly feature them.
How could I forget Laurie Metcalfe? She steals every scene that she’s in. I hope she’s featured a lot more next season, and that she and Judd Hirsch get together so that we see more of him, too.
That would be hilarious!
+1. 
Bob Newhart, Sara Gilbert, and Laurie Metcalf.
I can’t stand Leonard’s mother. Nothing against the actress, but the character is so toxic I can’t even laugh at her.
Laurie Metcalf I can’t stand. I knew too many people like her in West Texas, and there is absolutely NOTHING cute and comical about them. They should drop her pronto.
“Happy wife, happy life… let’s eat!”
Goodman would be excellent as Howard’s long missing father. And Parsons would have been so good as Sheldon’s Meemaw.
Parsons as Sheldon’s Meemaw is a many layered in-joke, seeing as how she’s a Parsons AND played Laurie Metcalf’s mom. Hey, maybe she really is Jim Parsons’ grandma!
Since it’s been established that Meemaw is Sheldon’s paternal grandmother, Estelle Parsons can guest star as Sheldon’s maternal grandmother (Mary Cooper’s mother) Estelle Parsons!
One great one that hasn’t been mentioned is Bernadette’s father Mike Rostenkowski, portrayed By
Casey Sander. For a man of few words, he manages to steal every scene he’s in.
Has no one mentioned Judy Greer as the slutty visiting physicist, Dr. Plimpton?
Dr. Slutbunny.
She’s always great.
She so much reminds me of the recently passed Glenne Headley.