Bicycle Forest - Wild tandem variants
 

I was going to respond to the thread on the NAHBS which mentioned the programmer of the Bike CAD software and had a picture of him, but then I decided that this warranted its own thread. The guy, Brent Curry, went to my old university, and my wife knows him quite well. He has designed and built many weird and wonderful bicycles, many of which are made for multiple people (although not all in the classic 'tandem' configuration).

Check out his website Bicycle Forest. Highlights include two tandem recumbents connected side-by-side (but which can also be ridden separately) to make a "Family Truckster" (click the link to watch a video of it in action):
http://www.bikeforest.com/Family_Truckster.jpg

He's also built an SUV / pick-up truck style vehicle to be their new corporate vehicle, the Rhoades Car (again, visit the link to watch a fun video):
http://www.bikeforest.com/rhoades_car.jpg
http://www.bikeforest.com/rhoades_car_rental.jpg

Another classic is the couch bike, seen here at a McDonalds drive-thru:

http://www.bikeforest.com/cb/drive_thru_couch1.jpg

If you live anywhere near Waterloo, Ontario, Canada (Google Maps, about 1 hour west of Toronto, 2-3 hours east of Detroit) then you can go along and rent one of his unique bikes - I can recommend the riding north of the city through the pleasant Mennonite farmlands.