The ZX81. My first machine. I also got (and repaired) one this Christmas.
Now, it's importance to the US is pretty nil, but this little machine was a huge deal in the UK.
See, it allowed you to own a computer for £69 (less than half of what anyone else was charging). That's really important and kickstarted the entire British gaming boom.
Many of the great UK games writers started out with the 81 and, for that reason alone, it does demand a little respect.
Sure, it had no color, no sound, some hardware issues, but that wasn't important then. It was a computer and that was enough.