Eagle Transporter from Mattel was the coolest sci-fi movie/TV tie-in toy of the 1970's... but the legendary 18" Alien action figure from Kenner is a close second - and I'm sure that many other Star Kids would rank it at #1.
And I might too, if I'd actually owned one. I do remember seeing one in the store in '79 and being both fascinated and frightened by it. I hadn't seen the movie - only coverage of it in Starlog and Fantastic Films - but I did ask my folks to buy it for me. Unfortunately once my mom glimmed the price tag and got a good look at the sheer grotesqueness of the figure, there was no way she was going to pick it up for me. Instead, I'm pretty sure I got a Moonraker space shuttle model kit... and, you know, I was pretty happy with that.
Ahhh... the Seventies.