The TV Series
In 1966, Star Trek debuted on NBC.  Over 30 years later, its characters are some of the most recognizable icons in Hollywood history.  Do I need to say more?

The Toys
After several attempts by other companies to produce a viable toy line, Playmates released in 1992 what would be the most successful Trek toy line ever. 

They were successful where other companies had failed in part because they featured larger-than-standard figures (for the times and genre, anyay), highly detailed likenesses of characters, multiple points of articulation, and perhaps most importantly,  because they saw Trekkers as an indication of a greater market of collectors.  Indeed, some folks (including a recent issue of Toyfare) have credited the Playmates Star Trek line with introducing the collectible action figure market. 

In recent years the 5" line has suffered setbacks, due in part to increased competition from other collectible lines.  Playmates tried to keep the Trek line alive by moving it into a new arena -- store & website exclusives, but currently it seems that the last of the Playmates 5" Trek figures has been produced.

Antedian

Bolian

Cheron

Efrosian (Federation President)

Pakled

Saurian

Selay

Tellarite

Commander Uhura

Lieutenant Ilia

A tip on customizing Star Trek Aliens...

Gene Roddenberry, creator of Star Trek, was once quoted as saying all Trek alien makeup, no matter how elaborate, should allow the actors eyes to show through.  His idea was that the real emotions of acting shine through the eyes.  Ok, I'm paraphrasing, but you get the idea.  If an actor's eyes could not be seen, he would look like little more than a walking plastic mask. 

So when I'm customizing a Trek alien, I always make sure that the base figure's eyes can "see" out of his newly scuplted mask, just like Roddenberry recommended. 

Thinking about customizing as if I were working on real actors helps in other ways, as well.   When adding details to a figure's head, I build up the layers as if I were a make-up artist working on a real person.  I make sure that the "actor's" head fits completely within the given "mask," which helps me keep proportions correct.  I don't sand down any areas beyond what would be a bald head -- after all, the aliens I'm customizing were originally played by actors, all of whom had to fit their heads completely within their masks. 

By combining the "see the eyes" technique with the "make-up artist" technique, I've managed to keep the scale of my aliens' heads proportionate to their bodies and to the other Trek action figures they are displayed with.