Bricker Jr asked me if there was any chance of the “Modern Family” characters visiting Pasadena and running into Dr. Sheldon Cooper.
I said the chances were vanishingly small. But it got me wondering: has there ever been a crossover that crossed networks?
Buffy and Angel come to mind, but they’re a special case because Angel was a Buffy spinoff and they began on the same network.
Any others?
Didn’t something happen between Community (NBC) and CougarTown (ABC)?
Boston Public crossed over with The Practice and Boston Legal. IIRC Boston Public was on Fox the other two were on ABC. I believe all were created by David Kelly.
Homicide (NBC) and The Wire (HBO).
Richard Belzer showed up as Munch in an episode of The Wire once.
The character has also shown up on Arrested Development & X-Files (Fox) and The Beat (UPN), as well as various incarnations of NBC’s own Law & Order series.
Kelly did it previously with Ally McBeal (Fox) and The Practice (ABC)
The final season of The Bionic Woman was on NBC, while The Six Million Dollar Man was on ABC. The character of Oscar Goldman was on both shows.
The Six Million Dollar Man and its spinoff, The Bionic Woman, both originally ran on ABC in the 1970s. For its final season, The Bionic Woman switched networks (to NBC).
At least according to IMDB, during that season, two supporting characters (Oscar Goldman, played by Richard Anderson, and Dr. Rudy Wells, played by Martin E. Brooks) appeared on both shows, on both networks. This was, apparently, the first time that actors played the same characters on different shows, on different networks.
Edit: ninjaed by RealityChuck, but I also got Dr. Wells. 
Dare I bring up Tommy Westphall?
There was a Seinfeld - Murphy Brown cross-over where Kramer was briefly Murphy’s secretary.
Yeah, I think his character Munch holds some kind of ‘official’ record for most appearances by the same character on different TV shows. Note that he played both himself *and *Lt. Munch in separate episodes of Arrested Development!
TV shows are more ‘owned’ by their production companies now than simply by the TV network that airs them, so if they share that it’s highly possible. Plus fans tend to really like it when they do this, the episode gets heavily cross promoted and usually high ratings, so it’s win-win (even if they’re not made by the same company).
I think Richard Belzer appeared on X-files and Arrested Development(both on Fox) as his other-network cop from one of the Law and Orders.
George Reeves showed up as the big guy for a CBS episode of I Love Lucy back when Adventures of Superman was in first-run syndication.
Was gonna say. 
Actually, the character originated on Homicide: Life on the Street. When that show ended he was hired for the first L&O spin-off SVU. According to Wikipedia the character ***does ***hold the record for most appearances on different series (ten different shows on five different networks!)
Ok, I’m familiar with the infamous St. Elsewhere finale, but how does it relate to crossovers? Did the Tommy character appear later someplace else? (I also know about the St. Elsewhere/Cheers/Frasier connection…)
The so-called “Tommyverse” incorporates hundreds of shows from multiple networks, including at least one Canadian network.
I don’t think that counts as a crossover. This was from the two- (or three?) parter where Kramer moves to LA to try a career in acting, and manages to get a bit part in one episode of Murphy Brown - Jerry and George are shown watching the episode.
Filthy Phil from Sons of Anarchy (FX) appeared on Raising Hope (FOX) in a cameo role.
Jimmy and Christine from Yes, Dear (CBS, cancelled in 2006) also made an appearance in Raising Hope this past week. They were part of a larger plotline.
Leaving the character of Tommy aside, St. Elsewhere also featured the character of Warren Coolidge, who had previously been a character on Bruce Paltrow’s CBS series White Shadow.
Didn’t two of the characters from Chicago Hope cross over to LA Law?
Two of the characters from the NBC soap Santa Barbara crossed over to LA Law, which ended in May 1994. Chicago Hope premiered in September 1994.
Then-Governor Michael Dukakis appeared on Saint Elsewhere, therefore the 1988 election was fictional.