I have alwasy been impressed by the design and support that West End Games (WEG) gave to their Star Wars Role-Playing Game. Sadly, in spite of all the good work, George Lucus went with the money and Star Wars became a d20 product. The d20 Star Wars is not bad, but it really does not fit the universe as well as the d6 system did.
Not wanted to let a good system go to waste, I started using the Star Wars rules for non Star Wars games. Metebarons, a game based on a series of comic books and graphic nvoels from Europe, is the latest incarnation of the d6 system. Metabarons is a very Heavy Metal-esque game. I love the world, but it's also a little over the top. And I mean E.E. "Doc" Smith over the top! Destroying universes, travelling the thousand galaxies, torturing your offspring to make them the next Metabaron.
Details on my more traditional Star Wars games can be found here.
A friend of mine used the WEG rules to run a firefly campaign.
I have used the Star Wars RPG along with Metabarons and Fading Suns to create my own space opera/science fiction game. I call it Honor of a Thousand Suns.