I seem to recall that when one of the writers wanted to work in a Andorian into an episode of TNG, someone told them, "We don't do antenna". Unsure if this is true or not, nor where I heard this, but the writer created the Bolians to have someone blue in it. They did once show an Andorian ...

The Inner Light.

...And Threshold, but that's for entirely different reasons.

I've always disliked the look of the Ori motherships in Stargate.

Stargate: Asgard
Star Trek: Andorian, Bolian, Gorn, Horta, Tellarite, Xindi
Star Wars: Ithorian, Wookie
Books: HP Lovecraft's Old Ones-Cthulhu fhtagn.
Forbidden Planet: The unseen Krell

I second Empire Strikes Back. Better than A New Hope, and it does not have something as obviously toyetic as the Ewoks in Return of the Jedi. I do find it a bit strange (or perfectly fitting, I can't decide) that the best movie is the one George Lucas had the least involvement in...