Babylon 5 is one of my all-time favorites, definitely. Londo and G'Kar made that show so f**king good, but it also helped how it had it excellent writing and a far-reaching plot that spanned whole seasons rather than just episodic content (not to say that's all bad, I just enjoy the other stuff more).
Farscape's another memorable science fiction series that I've come to love even more over the years.
That's about it. I enjoyed Star Trek stuff, I enjoyed even some of the Stargate shows, but none of them could compete with the aforementioned.