Jump!

One of my favorite things about the Internet is the power it has to give handy common language. For example, jumping the shark. Most every TV show hits a point where it all just starts to fall apart. The point at which the thing goes from being a good show to being totally past its prime. The term was made famous by John Hein, founder of the now defunct jumptheshark.com, in reference to an episode of Happy Days, in which the Fonz, clad in his signature leather jacket, leaps, on water skis, over a shark in a daring display of manliness.
Often the shark-jumping moment is some last ditch effort to salvage a sinking ship - like  little cousin Oliver on The Brady Bunch, brought in because apparently Cindy wasn't cute enough. Or Scrappy Doo. 
Or sometimes it's that an actor left a show on bad terms, and they have to do something to explain their absence (or not, in the case of the older brother in the first season of Happy Days). Like half the cast of Three's Company.
A few shows have run with this. The X-Files had an episode in their final season called Jump the Shark, although I think we can all agree that The X-Files jumped long before that episode aired. The Simpsons featured an episode in which Homer actually recreates the Happy Days shark jumping scene, and one of the final episodes of Pushing Daisies features an underwater circus act involving a performer jumping over a shark.
Ted McGinley, the suave sailor pictured below (check out that awesome Ken doll hair), has been called The Patron Saint of Shark Jumping because of how often he appears in shows that are in the process of jumping. Like Happy Days. It seems Happy Days did a lot of jumping. According to Wikipedia, McGinley made a reference to this on Married...with Children, in which he once refers to Al as Fonzie. 

Other ways a show can jump, according to the aforementioned defunct jumptheshark.com, include the following (whether the examples given are jump-worthy is up to you to decideO:

• Same Character Different Actor: The famous Darren switcheroo on Bewitched, and Second Becky on Rosanne. Second Becky, played by Sarah Chalke of Scrubs after the original Becky left the show. Oddly, the original Becky, Lecy Goranson, came back to the show after a while, and instead of getting rid of Second Becky, they alternated the two actresses. Who look absolutely nothing alike.
• They Did It: Two characters whose sexual tension drives the plot along finally hook up. Like Pam and Jim on The Office. Tony and Angela on Who's the Boss. Then again, there's The X-Files, in which the unresolved sexual tension goes so long unresolved you stop caring whether it ever happens.
• New Baby: Rachel gives birth on Friends, for instance. Or Fran on The Nanny. Did she give birth, or did I dream that? It was on really late at night, back before the days of cable, and I used to fall asleep to it. That or stupid Matlock.
• The Wedding: Lisa and what'shisface the evil dude on News Radio. Rhoda and Joe on Rhoda.
• Radical change: Rosanne wins the lottery. Sacred Heart Hospital on Scrubs inexplicably transforms into a med school. Laverne and Shirley move to LA, bringing the entire supporting cast with them. TVTropes.com refers to situations like this as a reboot, which I love.
•  It Was All a Dream: Absurd on Dallas. Brilliant on Newhart. 

How about you? What's your favorite shark-jumping moment.