Thomas Magnum on JAG would have been perfect and a sort of passing of the torch for Bellasario's leading men. The plot writes itself...Magnum working for Navel Intelligence somehow gets entangled in a JAG case...too easy.
Well, there's always NCIS...same producer(s), right?
Would have enjoyed seeing President Jed Bartlet being briefed on the Stargate program.
A Voyage to the Bottom of The Sea
crossover. Even something small like the Seaquest being tasked by the Nelson Institute or something.
How about an ER
crossover where Benton brings Ray into County General for something and they get involved in some sort of goings on at the hospital?