Space Master by ICE was one of my favorites for years.
Now I run D20 Future and pull in all KINDS of sources and just toss proprietary notions out the window.
As an example... I had a pirate group of Klingons piloting old Tie Fighters and a YT-1300, with a couple of Cardassian and Kilrathi crewmen thrown in for variety.
So far, my players have encountered (in the D20 Future game):
Predators
Klingons
Zerg
Kilrathi
Cardassians
Klendathu Arachnids
Interdimensional Fomorians
Ogres
Elves
Dwarves
Ng-Kher-Arla (bonus points to whomever can name that source without resorting to a search engine)
Space bound pot-heads (they're currently in the midst of delivering bales of "baled organic material" to New Amsterdam... and yes... I know that was the original name of New York, but now it's not, and it fits the theme of the place I needed.
And Star Patrol (Star Frontiers) has recently approached them regarding deputization.
This is all set in a backdrop of what amounts to Space Master political boundaries.
If it's Sci-Fi, it's possible game fodder for my D20 Future game.
So, yeah... I say D20 Modern, D20 Future, D20 Apocalypse, Darwin's World 2, and anything you want to use as source material.