Naturally, only a small fraction of these have been explored in the Star Wars universe to date. Many more will be explored and catalogued, as the reading public's appetite for endless spin-off trilogy novels shows no sign of being slaked.
Let's take a tiny fraction of those, and say that 50,000 sentient biological life forms have been mentioned, even second- or third-hand, in every single corner of the canonical Star Wars universe. This includes not only the movies and the books, and the aforementioned spin-off trilogies, but also the many video game universes and role playing games.
50,000 sentient biological life forms sounds like a lot, but it's only 1/400th of the species available to us.
Doesn't it seem a bit odd that out of those 50,000 intelligent biological life forms, all but ten hew to the standard binary male/female pattern of sexual dimorphism? The Wookipedia goes so far as to broadly define the gender terms as "impregnator and gestator," but this is just a semantic game.
It begins to look less like a conspiracy by the heterosexual hegemony and more like a failure of imagination when the Wookiepedia points out that most females have breasts and are smaller, and most males are larger with broad shoulders and deep voices. For all intents and purposes, aliens in the Star Wars universe are just people with funny costumes. Which is understandable in the movies, where special effects cost money. Less understandable in video games and fiction, where words and pixels are cheap.
The non-heterosexual species are:
- Hutts (hermaphroditic)
- Pui-ui (hermaphroditic)
- Verpine (hermaphroditic)
- Strills (hermaphroditic)
- Vratix (a gender-changing species with two genders; each individual spends half their life as one gender, and half their life as the other)
- X'Ting (ditto)
- Xi'Dec (an insectoid species with over 180 million different genders)
- Filordi (asexual)
- Fnessian (three genders)
- Rakririans (three genders)
And now we come to the oddest and most interesting part of this discussion: the reason why I have been specifying "biological life forms." Surely no one will question the sentience of C3PO! The Wookipedia entry on gender thoughtfully includes a passage on droids.
I had never thought about droid gender, but clearly some droids have been programmed with distinctly male or distinctly female characteristics. C3PO seems clearly to be male, although R2D2's gender is still up for debate. However, "an official source indicates that the droid has masculine programming."
There are several examples of overtly female droids in the Star Wars universe, as well. I had forgotten about the female droids which attended to Bail Organa, but the official Star Wars databank includes an entry which fairly pants with excitement at the BD-3000 Luxury Droid's "chromed finish, smooth surfaces and eye-pleasing shape."