Hmm, thats a tough one. Dont watch a lot of sci-fi series. Actually closer to zero than just one.

With good chance of offending a lot of people, I would say Stargate is a complete waste of time.

I have only watched two episodes of Firefly, but I would say it is pretty cool. More of a western actually.

Does the X-files count? Because thats one of my favorite series of all time. And also one of the few I actually liked. Some were better than others, but those that were good are forever imprinted in my memory!