7. Newhart
Back in the 80s, Bob Newhart starred as Dick Loudon, an author of DIY books in the television show Newhart. They were at it for eight years, when the show was finally cancelled in 1990. What ensued was one of the most frustrating and memorable series finales in history. On the show, their small town is purchased by a wealthy Japanese tycoon with plans to turn it into a golf course and resort. The Loudons are the only townspeople who refuse to accept the massive payout, and stay on to run the Stratford Inn. Then one day, Dick Loudon is minding his own business when BAM! He gets hit in the head by a golf ball from the course. The screen goes black, and the next thing we see is Bob Newhart waking up... as Dr. Robert Hartley, in his bed on The Bob Newhart Show, which had been off the air for about twelve years. He turns to his wife Emily and says: "You're never going to believe the dream I just had!" To sum up, the producers decided to make the entire run of their show just a dream of a character on another show. Excuse me while my brain explodes.
How It Should Have Ended... Actually, I'm pretty OK with this. It's so far out of left field that it works.