First model kit ever: Snap-tite space shuttle. I was about 6. Turned out crappy.
First model kit in "modern times": Star Trek: Deep Space Nine Runabout. About 8 years ago. Turned out decent because the guy at the shop told me to use a spray can for the base and acrylics for the details. Works good. I still do it that way when I can.
Built one "car" during my sci-fi period: the AMT BTTF Delorean. I think I killed it though...
First kit of current automotive enthusiasm: Tamiya Honda S2000.
I've had it for about three years but it's still not done yet for some strange reson...