http://en.wikipedia.org/wiki/TRS-80_MC-10
Out of all the Tandy stuff, maybe this one as it was only made for 1 year. One of these was my very first computer. I couldn't have been more than 8 years old and I learned to program basic on it. I'm not sure if they will ever be worth much, but I'd sure love to have one again. I had a cassette drive for it too and a couple of tapes with some primitive games. I have no idea whatever happened to mine. I guess my parents must have sold it long ago.