
At least sixteen of RSL's former co-stars have ended up with guest roles on House (last four in the list below were ID'd by Muggs on HHOW).
Sasha Alexander ("The Down Low", was Jesse on the TV series "Wasteland" - RSL played the character named "Jesse's ex" in one episode)
Eddie Mills ("Clueless"; in that episode of Wasteland with RSL)
John Laroquette ("Son of a Coma Guy"; in Corsairs with RSL)
Scott Foley ("Sports Medicine"; in a play with RSL)
Cynthia Nixon ("Deception"; in The Manhattan Project (and plays) with RSL)
Kurtwood Smith ("Half-wit"; played RSL's father in Dead Poets Society)
Frank Whaley ("Mirror Mirror"; in Swing Kids, and in plays with RSL)
Piper Perabo ("Resignation"; in The I Inside with RSL)
Kip Pardue ("Forever"; in Driven with RSL)
Brent Briscoe ("Three Stories"; in Driven with RSL)
Mackenzie Astin ("All In"; in Last Days of Disco with RSL)
Geoffrey Lewis ("One Day, One Room"; in A Painted House with RSL)
Dylan Kussman (the father in "Kids"; in Dead Poets Society)
Jack Plotnick (Hal Connor in "Broken"; in Ground Control)
Jonathan Fraser (motorbike salesman in "Autopsy"; in Ground Control)
Stacy Edwards (Lucy Palmeiro in "The Socratic Method"; in Driven)
ETA 4/27/10:
Ann Dowd (Mother Superior in "Damned if You Do"; in the play Candida with RSL)
David Strathairn (POTW in "Lockdown"; RSL's father in In the Gloaming)
Stated another way, over 10% of House episodes have had a former RSL co-star in it. O_O
Anyone know any more? We might've missed out on some who were on the stage with him.
PS. If there are any other guest stars in future episodes, DON'T MENTION them. No spoilers please.