This isnt very "modelish," but the K'nex roller coaster is interesting. I
own one, and I built the normal looping model. I soon tore that down and
had it circle 2/3's of my room. I had the loop at the end, but soon turned
it into a corkscrew.
Its a bit childish, but REALLY fun to build. Yes, you can make a little
car go around it. The size of the model is 3ft high, about 20 foot long
track. My own encircling model starts at 7ft, ends at ground floor. Its
not a complete circuit. The planned model is, and it has a chain "crank"
lift. I, however purchased the motor so I can stare at the roller coaster
for endless hours.
-http://members.aol.com/mrbill1058/g.html <--ROLLER COASTERS!!!