There was a Charlie's Angels where one of them gets accidentally grazed in the head by a kid playing with a real gun and gets amnesia. It was a direct reuse of a script from a Mod Squad ep (Julie was hit in that).
Then there was that TNG ep where Riker is accused of murdering an alien scientist to get his wife, and they reenct the crime on a holodeck. The same script was recycled on Voyager with Tom Paris in the hot seat. Can't recall either ep title at the moment.
And if you wanna see a complete theft, watch the closing scenes of Babylon 5's "Mind War", then watch the closing scenes of Voyager's "The Gift." Complete. Rip. off.