Nowadays, the only one that comes mind right away is "Law & Order", with occasional visits by other cast members on "L&O" shows they don't usually occupy.
In the past, I recall folks from "Petticoat Junction" would visit on "Green Acres." I also once saw Stu Bailey of "77 Sunset Strip" visit a soundstage while "Maverick" was being filmed with Roger Moore. An outright plug was a visit/guest by Ty Hardin of "Sugarfoot" on "77 Sunset Strip." Another time, a "Maverick" had cameos from members of "Cheyenne", "Lawman" and "77 Sunset Strip!" Once in cartoon-land, I recall Yogi Bear being in someone else's toon, with Yogi stating, "I gotta go...I'm on the wrong show!" What other "visits" do you recall?
In the past, I recall folks from "Petticoat Junction" would visit on "Green Acres." I also once saw Stu Bailey of "77 Sunset Strip" visit a soundstage while "Maverick" was being filmed with Roger Moore. An outright plug was a visit/guest by Ty Hardin of "Sugarfoot" on "77 Sunset Strip." Another time, a "Maverick" had cameos from members of "Cheyenne", "Lawman" and "77 Sunset Strip!" Once in cartoon-land, I recall Yogi Bear being in someone else's toon, with Yogi stating, "I gotta go...I'm on the wrong show!" What other "visits" do you recall?