This ZX81 advert is included in a bunch of ‘Hilariously unimpressive computer ads’ on Oobject.  Maybe it seems unimpressive now, but this advert probably made my dad go out and buy one, and that probably went a long way to making me fall in love with computers and technology.

oobject » Finally you can afford to satisfy your lust for power - A ZX81 with 1K of RAM