The only one that came to my mind was Bugs Bunny.
Charlize Theron and Liza Minelli, both in Arrested Development.
Kathy Bates was in Six Feet Under and The Office.
Mercedes Ruehl had a guest run on Frasier.
Sister Pete!
Mel Brooks - Best Original Screenplay for The Producers (1968), later made three television series: When Things Were Rotten (1975), The Nutt House (1989), Spaceballs: The Animated Series (2008).
Helen Hunt won her Oscar for As Good As it Gets while she was still appearing on Mad About You.
One of the first Oscar winners to do a TV series was Shirley Booth- from Best Actress in ***Come Back, Little Sheba ***to wisecracking maid in the sitcom Hazel.
Well Adrien Brody has been showing up in some pretty terrible commercials lately.
**Forest Whitaker **was in a short-lived series in 2011 called “Criminal Minds: Suspect Behavior.”
Charlton Heston starred in the Dynasty spinoff The Colbys.
Does Jose Ferrer count as a TV series regular, for his appearances on Newhart?
There was Richard Dreyfuss on the short-lived drama series The Education of Max Bickford.
Also…
F. Murray Abraham has appeared recently on Homeland.
Marcia Gay Harden is on The Newsroom (and has appeared in other TV series since her Oscar)
A few years after winning Best Actor for playing Idi Amin, Forrest Whittaker took the lead role in a Criminal Minds spinoff.
The TV series itself has been forgotten, but Hattie McDaniel, who won an Oscar playing Mammy in Gone With the Wind, starred in the early Fifties sitcom Beulah.
Like Amos & Andy, the sitcom was widely regarded as perpetuating racial stereotypes, so as far as I know, it hasn’t been shown in re-runs in my lifetime.
George C. Scott played the President in Mr. President, an early (and short-lived) Fox network sitcom. (Yes, he counts as an Oscar winner; in fact, I remember a picture of Scott holding it, standing next to Charles Finley (longtime owner of the Oakland Athletics).)
He was also Ebeneezer Scrooge in a made-for-TV version of A Christmas Carol back in '84.
Christine Lahti also won the best live action short film award, while she was on Chicago Hope.
Also, Jim Rash won the Oscar for best adapted screenplay for The Descendants in 2011, while appearing on Community as Dean Pelton.
Shelley Winters won Oscars for The Diary of Anne Frank and A Patch of Blue. Estelle Parson won an Oscar for Bonnie & Clyde.
Then they portrayed Roseanne’s Nana Mary and mother Beverly Harris.
Broderick Crawford – On TV with Highway Patrol.
F. Murray Abraham – Homeland
One which I should have thought of in hindsight was Patty Duke, who won an Oscar for “The Miracle Worker” in 1962 at the age of 16, then starred in “The Patty Duke Show” and a few other series afterwards.