One of the last things Alaska Gov. Walter Hickel did before he resigned to join the Nixon Cabinet was to fill a Senate vacancy caused by the December 1968 death of E.L. Bartlett, a Democrat. Hickel picked a GOP state representative by the name of Ted Stevens. Stevens, who only months before lost a Republican primary bid for a different seat, went on to serve more than 40 years in the Senate, longer than any Republican in history. Appointing Stevens was by any definition a good move.
Less successful was Illinois Gov. Rod Blagojevich's opportunity some 40 years later to fill a Senate seat. With Barack Obama having been elected president, Blagojevich decided to offer the seat to the highest bidder. By doing so, he got himself impeached, removed from office, and sent to prison. It was also the beginning of the end for Rep. Jesse Jackson Jr., a rising star who ultimately was brought down thanks to his own greed and crashed to Earth (and served time as well).