Abscam is one that sticks in my mind but the age of that particular scandal and that I recall it tends towards a proof of the contention that it is rarer.
Another thought: For the past several days, some honesty-in-government types have been reminding everyone about the ethics questions concerning Murtha that go as far back as his alleged involvement in the Abscam scandal in 1980.
There was ABSCAM in 1980, when the FBI set up a sting operation that caught on videotape a senator and five representatives receiving cash payments from a fictitious Middle Eastern businessman in return for political influence.