RAWDuke in many cases you can catch a flight out of Tupelo, fly to Memphis and then to another point, cheaper than you could fly out of Memphis to that point. Sound impossible? Well there is a charge (tax?) included in all tickets that goes to the airport. It is the originating airport that gets it. Memphis imposes a much larger charge than Tupelo. This became a problem for the airlines, because people would buy a ticket from Tupelo and then just go to Memphis and catch a plane. Now they have a way of checking that you actually took the first leg of the trip.
Atlanta to Macon, GA - under 90 miles. This was back in 1974 on an honest to God jet (a DC-9), and I don’t think the plane even levelled off. I think the flight took about a half hour.
I’ve flown from Madison to Milwaukee (about 70 miles) several times. Siince Madison’s airport is a regional, you usually have to go somewhere nearby (Mpls, Chicago, or Milw) to get your flight.
Do stopovers count? On a flight out of Ithaca, NY, our plane stopped at Elmira, NY all of 33.5 miles away by car according to maps.yahoo.com. On the return flight, they made us get off in Elmira to service the plane before continuing on to Ithaca. I believe my wait at Elimira airport took longer than the hop to Ithaca.
I’ve flown from BWI Airport to Dulles Airport, which must be under 50 miles as the crow flies.
That was on a relatively small turbo-prop pplane. My shortest flight on a large jet was from Philadelphia to BWI, which is less than 100 miles.
Boston to Boston, net distance zero but it took 2 hours. We took off for Montreal, reached a point over the city, found out the runways were iced over, and diverted to the place we left. Didn’t even get the Delta Frequent Flyer miles.
At one time, Air France scheduled a regular flight from Basel, Switzerland to Mulhouse, France, continuing to Paris Orly as a domestic flight. Scheduled time: 1 minute. Basel and Mulhouse are the same airport. It never physically left the gate. The duty-free sales must have been eyepopping, though.
The US Airways - Allegheny Commuter schedule used to list service from Northeast Philadelphia to Philadelphia International, still within city limits - with a plane change in Pittsburgh.
The late, great Island Airways once served Bass and Kelley Islands in Lake Erie with Ford Trimotors out of Port Clinton, and advertised itself as The World’s Shortest Airlines.
The shortest real flight you can get now is on Loganair between the Scottish islands of Westray and Papa Westray. It’s scheduled for 2 minutes but has been done in less than 1.
5 miles - Cayman Brac to Little Cayman, following a 90 mile flight from Grand Cayman. Thought it’s debatable whether Island Air counts as a commercial airline…
I forgot to mention I once took Allegheny from Boston to Columbus, on a BAC111, with stops in Albany, Buffalo, and Cleveland. They almost didn’t bother to retract the gear.
How about long short flights? Boston to Boston via Montreal counts. When I lived in Louisiana the only way to fly from Lafayette to Houston was by way of New Orleans, 100 miles in the wrong direction. 
That was scheduled. I once had the wonderful experience of flying from Austin to Houston, discovering Houston was closed due to a storm, going to New Orleans for gas (why they didn’t stop in Baton Rouge or Lafayette I don’t know - maybe New Orleans gave more green stamps) and then back to Houston, where they cancelled the flight. The poor lady sitting next to me had gone to Austin to file some court papers, not telling her family, and was freaking out because her mother must have thought she had disappeared for hours.
Dallas to Houston, about 240 miles.
Ontario, CA, to John Wayne, Orange County.
Ontario, CA, to Burbank
Phoenix to Tucson
On small, turboprop planes:
Lincoln to Omaha, Nebraska
Rochester, MN to Waterloo Iowa
Chicago to Janesville, Wisconsin
On full-size jets:
Atlanta to Albany, GA
Indianapolis to Chicago
Lexington, KY to Cincinnati
Detroit to Grand Rapids, MI
Back in the days before airline deregulation, it wasn’t unheard of for small, regional airlines to fly to cities only 30-40 miles apart, Using equipment like Boeing 737s instead of the DC-3 aircraft they had originally used on those routes.
Cicada2003 you probably recall reporters talking about John F. Kennedy’s assasination. He had started the day in Ft. Worth and then flew to Dallas. In fairness, he did fly from Carswell AFB, on the west side of Ft. Worth. However, for a brief time there was airline service at both Fort Worth Greater Southwest Airport (located right at the edge of what is now DFW) and Dallas Love Field, and the airlines flying to those cities did have flights which stopped at both airports. I think the flying distance between them was something like 16 miles.
My very first time flying was:
Lincoln, NE --> Omaha, NE --> Chicago, IL --> Indianapolis, IN
Each hop was on a 737, IIRC, and each hop was really short, relatively speaking. The Lincoln-Omaha hop only seemed to take a matter of minutes since most of the flight consisted of taking off and landing.
Pittsburgh to Columbus, 185.5 miles. It was a stopover on the way from San Francisco. Why I had to overshoot my destination by 185.5 miles, I have no idea. the flight was so short that as soon as we were in the air, the airline attendants started the beverage service, and they weren’t done collecting the cans when we landed, twenty minutes or so later.
When I lived in Houston and was travelling for work a lot, I would sometimes take a Continental Express flight from Ellington Field on the south side of Houston to Intercontinental on the north side where I would connect with my main flight to wherever I was going. This is about 37 driving miles and about 23 nautical miles.
Can I hijack this for a moment for a GQ-type question, since we’re already more or less on the topic?
Basically: why is it so often cheaper to fly out of the way, have a brief stopover elsewhere, and then continue on to your destination? Example: last time I flew out to Denver, the cheapest fare went Philadelphia-Minneapolis-Denver and back the same way.
And also, in recent news, it’s apparently cheaper for me to drive down to Baltimore, get on a flight at BWI, stop in Philadelphia (20 minutes from my house), and continue on to Dayton, OH. Same flight. They charge me two hundred bucks more to spend twenty minutes less on the plane?
Shortest flight: Arnold Palmer Regional Airport in Latrobe, PA (home of Rolling Rock beer and, uh, Arnold Palmer) to Pittsburgh International on US Airways. I did it just for kicks, I even checked a bag, just to see how long it would actually take.
My husband dropped me off at the front door of the Latrobe airport so that I could check in right at the mandated time, and drove to the Pittsburgh airport to pick me up.
It’s 62 miles by road, but once I went through security on the Latrobe side, boarded, taxied, flew, landed, taxied and then walked the 22 miles from the gate to the baggage claim and then the pickup area in Pittsburgh, Mr. TeaElle had been forced to circle the airport drive twice before I was ready to be picked up.
(There were several flights between the two airports daily until just recently – they’ve become a casualty of US Airways pisspoor fiscal management. Damn shame, that, LBE was a nice option for people living in Johnstown and Altoona, but now they’re forced to drive that extra ~100 miles to fly directly out of PIT.)
I’m curious about this flight in the Orkneys. Is it because they are two separate islands or are you Brits just weird? (Or both?)
Two shortest flights I’ve taken:
From Copenhagen to Malmo. They’re across the Oresound (sp?) from each other, and it used to be you could fly or take the ferry. The ferry is also nice because you can enjoy the view and have some beers.
From Nantucket to Cape Cod. Probably also about 15 minutes. This one was cool because I got to sit in the copilot seat and watch the flight out of the front window. Our pilot didn’t look like a Hollywood actor (like on Wings), he looked more like a guy who’d seen the inside of a bottle more than a few times and might have trouble keeping a major airline job.
Shortest international flight I’ve taken:
From Frankfurt to Brussels. It’s about 40 minutes. We joked that the jet had to circle the airport a few times so they’d have time to give the landing annoucement in English, French, German and Flemish.
Yes they’re separate islands - and it’s a service which continues to other places. Photos here.
Although for the record, Orcadians are very weird indeed 