The Archers had a crossover with Gardener's Question Time for Easter 2011, where the real-life panel, chaired by the real-life Eric Robson answered questions from the population of Ambridge.
On the April 1, 2013, broadcast of "Family Life Today", John Fuller and Jim Daly, from "Focus on the Family", crossed over.
Two episodes of The Goon Show featured guest appearances by Jack Train as Colonel Chinstrap from ITMA, a popular comedy show from the previous decade. There was also a crossover with the comedy "Educating Archie", called "Archie in Goonland".
An arguable one, similar to the Comic ReliefPanel Game crossovers above, the New Year 2010 episode of The BBC Radio 4 comedy panel game The Unbelievable Truth featured Stephen Fry, Alan Davies, regular QI panelist Rob Brydon and QI producer John Lloyd. The format of the game was unchanged, but the "obvious answer" klaxon was added. Much to the satisfaction of the other players (and host David Mitchell), Stephen set it off twice.